Broadcast Zones

7/29/2019 Broadcast Zones

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Storage-centricIf youve got

one storagecabinet attached

to many

Broadcast zonesA broadcast zone behaves similarly to a VLAN that is created usinga protocol suchas the AppleTalk VLAN discussed previously. Since

Fibre Channel can carry bothSCSI and IP traffic, you can create a

zone that consists only of those HBAs that sup-port (or wish tocarry) IP traffic. However, unlike protocol-based VLANs thatcanautomatically add a server to a VLAN if its using a particular

protocol, a broadcastzone is merely a functional classification.

Current zoning technology doesnt sup-port automatically adding amember to a zone based on its protocol. A broadcastzone is merely asoft zone that contains the HBAs that communicate with a particu-lar

protocol.

Naming your zones

Just as creating aliases for the ports on your switches and arrayshelps you identifythe m, usi ng an app rop riat e n ami ng

conven tion for your zones can help too. You should pick a namethat reflects how the zones are being used. Two common nam-ingconventions are called

server-centricand


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storage-centric.

Server-centricIf youve got a SAN that consists of many storage arrays connected to one

server,the zone should be named after the server. This is referred toas a server-centriczone-naming convention.

Storage-centricIf youve got one storage cabinet attached to many servers, name thezone afterthe storage cabine t . This is refe rred to as a s torage -centric zone -naming con -vention.

LUN MaskingAlthough logical unit number (LUN) masking isnt technically atype of zoning, itdoes perform a similar function. It keeps differentservers from seeing or using eachothers storage on the SAN. However,

before explaining how LUN masking and zon-ing are different, we mustdefine LUN masking. And before we do that, we must firstdefine a LUN.ALUN is a logical representation of a physical unit of storage and mayrepresent anyof the following: Physical disk Physical tape drive


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Robotic control device Logical disk consisting of many physical disksstriped together Logical disk consisting of two mirrored stripes This is the Title of the Book, eMatter EditionCopyright 2011 OReilly & Associates, Inc. All rights reserved.

52|C h apte r 3 : Manag i ng a S A N

Each Fibre Channel storage array or tape library may have multiple ports that

can beconnected to the SAN, each with its own WWN. The array will also beconfigured torepresent its storage as LUNs attached to these WWNs.Therefore, each array wil la pp ea r to t h e ho st s o n th e SA N a son e o r mo r e L U N s a t t a c hed t o o ne o r mor e WWNs.LUNmasking hides, or

masks, LUNs s o that each s erver se es onl y the LUNs you want i t tosee. LUN masking is actually performed at a level just above

zoning. Azone grants or restricts access only to a given

porton a storage array, but LUN mask-in g can ta ke that port and grantone ser ver acc ess to som e of its LUNs and gra nt another server

access to the rest of its LUNs.Su pp os e yo u hav e a si ng le -p ort edstorag e ar ray w ith a nu mber o f di sks, some of which you wantto use on one host and some you want to use on a second host.

Inorder for this to work, you need to create a zone that gives both servers


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access to thesto rage arr ay. Howe ver , not hin g prev ent s the firs tserver f rom using the second servers disks, which is what LUNmasking is for. LUN masking allows you to selec-tively present half the

LUNs to the first server and half to the second server.Depending on which

vendors you use, LUN masking can be performed on one of threelevels:

Storage arrayA storage array can be configured to present certain LUNs to certain hosts.

Oneway this is done is through offsets. Suppose a storage array has atotal of 100LUNs. Connected to that storage array via a switch are five

hosts, and you wanteach host to see 20 of the 100 LUNs. Youconfigure the array so that LUNs 1through 20 are displayed to the first

server, LUNs 21 through 40 are displayed tothe second server, and so on.

The first server then sees LUNs 1 through 20 anddoesnt see LUNs 21through 100; they have been masked from its view.

Intelligent bridges and routersIf you use a storage array that doesnt support LUN masking,

another way toaccomplish it is to place an intelligent bridge orrouter between the servers andthe storage. Then follow steps similar tothe ones just described.


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HBA driversLUN masking performed on the HBA level places the responsibility formaskingthe undesirable LUNs on the HBA driver itself. Although the HBAcan see all theLU Ns avai lab le on the SAN , y ou conf igur e the

driver to mask the LUNs you dont want it to see. Once this hasbeen done, the driver presents to the operat-ing system only the LUNsyou want it to see.

Designing Your SAN for

AvailabilityOne issue with traditional parallel SCSI that can be solved by SANs is that ofhavinga single point of failure. Everyone knows that the failure of a single

SCSI card, cable,This is the Title of the Book, eMatter EditionCopyright 2011 OReilly & Associates, Inc. All rights reserved.

Access to Storage Resources|53

or terminator can render your parallel-based SCSI devices useless.With SANs, youcan use multiple paths to ensure that no single

device can do this. However, manypeople design their SANs just asthey design their parallel based SCSI systemsonepath to each


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device. Consider the SAN depicted inFigure 3-3.In the figure, each serverhas only one path to each storage array and tape library.Each path hasat least 11 single points of failure, as shown by the numbered arrows:1.

The servers HBA2.The Fibre Channel conductor from the server to the first switch3.

The incoming GBIC on the first switch4.

The first switch5.

The outgoing GBIC on the first switch6.

The Fibre Channel conductor from the first switch to the second switch7.The second switch8.

The incoming GBIC on the second switch9.

The outgoing GBIC on the second switch10.

The Fibre Channel conductor from the second switch to the storage array11.


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The controller on the storage arrayFigure3-3.Single points of fai lure in a s ingle fabric1234568791011

This is the Title of the Book, eMatter EditionCopyright 2011 OReilly & Associates, Inc. All rights reserved.


Besides having 11 single points of failure, there are several pieces

of equipment thatneed preventative maintenance at various times,such as firmware upgrades, driverupdates, and hardwarereplacement. The only way to do any of these things is totake down at

least one systems storage. If the piece of equipment that needs mainte-nance is one of the switches, then several systems will be withoutstorage during theupgrade.You can create a SAN that has no

single point s o f fa i lure and can be maintain ed without a serviceinterruption by designing a SAN that looks more like the one

inFigure 3-4. You can see that every server has two completely

separate paths to eachstorage resource, as depicted by Path A andPath B for the server on the left side of the drawing. If any piece of

equipment along Path A fails or needs preventative main-tenance, Path Bwill take over immediately until that piece of equipment is

returnedto full functionality.

Multipathing


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Once youve designed a SAN with multiple paths, you need sometype of softwarethat understands you have multiple paths and knowshow to use them. The reasonfor thi s is tha t dee p ins ide eve ry

SAN is the SCSI protocol, and SCSI was neverdesigned with

multiple paths in mind. This means you need a piece of software tositbetween the SAN and the operating system and present only one path tothe operat-ing system at any one time. This is the job of multipathingsoftware, and there areF i g u r e 3 - 4 . A m u l t i p a t h S A NPathAPathB

This is the Title of the Book, eMatterEditionCopyright 2011 OReilly & Associates, Inc. All rights reserved.

Access to Storage Resources|55

dozens of such products now on the market. Here are a fewexamples in alphabeti-cal vendor order:Compaqs Secure Path

EMCs Power Path Solaris 8 has native multipathing support

Veritas Volume Manager has multipathing support Vicoms StorageVirtualization EngineMultipathing software actually performs two

functions: automatic failover and loadbalancing.

Automatic failoverPerhaps the most important job for multipathing software is toautomatically redis-tribute I/O to another channel in the case offabric failure. This should be done insuch a way that the operating


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system never realizes there was an interruption in ser-vice. This, ofcourse, needs to be done within the limits of a SCSI timeout.

Load balancingThe second important job multipathing software performs is

dynamic load balanc-ing. Many administrators perform this taskmanually using

staticload balancing.That is, they take an inventory of the various paths a

particular server has to its SAN-at tached disks and then use thedif fere nt nam es of t he dis ks to bal anc e th e l oad between the

various paths. Dynamic load balancing, however, can be done onlywithmultipathing software, because such software sends a given stream of

data down theleast-used path. This allows you to fully utilize all paths when

the SAN is completelyfunctional. Then, of course, if a given pathbecomes nonfunctional, there is simplyone less path for the load

balancing software to use.

Preventing thrashingWhat happens when a given path goes up and down multiple times?

Without sometype of antithrashing setup, multipathing software might justgo a little crazy. Thereare a few different ways to keep the system from


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thrashing in this manner. The first isto configure the software toreenable a previously fai led l ink only after a certainamount oftime. If the link goes back down while the software is waiting to

reenableit, the clock starts over again. Another common method is to set up

the SAN in sucha way that a failed link must be reenabled by anadministrator after she is convincedthat link is healthy again.This is the Title of the Book, eMatter EditionCopyright 2011 OReilly & Associates, Inc. All rights reserved.


Persistent BindingOnce zones and LUN masking have been set up , each server

should see i ts s tor-ageand only its storage. Once this has beendone, one initial setup task remains.I t s al ready been ment ioned

that on e of the i ssues wi th SANs is that serv ers can sometimeschange the SCSI address of a particular unit of SAN-based storage.

Thisis particularly true if the configuration of the SAN changesbetween reboots. Again,this is caused by the assumptions the SCSIdrivers make about targets they see.The upper levels of all devicedrivers used in a SAN environment are designed forSCSI. The SCSII/O model assumes a small number of targets on a single bus and


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asmall number of LUNs on each target. In order for SCSI addresses toremain perma-nent, they need to be bound to an address that doesntchange.As discussed inChapter 2, when a device logs into a fabric, its also

assigned a sourceID (S_ ID) by the fab ric sw itc h. Whe n a devi ce

connects to an arbitrated loop, itselects an arbitrated loop physicaladdress (AL_PA) during the initialization process.The S_ID and AL_PAare similar to IP addresses in a DHCP environment. Theyaredynamic, and so therefore shouldnt be used to generate SCSI

addresses.The unchanging target address of a SAN-based storagedevice is the 64-bit WWN.Similar to the MAC address with Ethernetdevices, the WWN is a permanent num-ber as si gned to each po rt

on a s torage array or an HBA on a server . However ,asmentioned previously, a SAN-connected RAID array may have

hundreds of disksthat need to be individually addressed by servers.Therefore, the RAID controller cre-ates LUNs for each device. Each LUN

has a corresponding WWN assigned, which isa subset of the masterWWN assigned to the RAID controller. These LUNs are usedb y th eoperat ing system as a SCSI address and mask the unde rlying

use of RAIDtechnology.Binding is the process of associating theoperating systems controller, target, andLUN value to the WWN of


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the LUN created on the RAID array controller. Bindingtakes place onthe device driver level; the unique WWN value is

boundto an operat-ing-system controller-target value. When this bind i s

persistent from boot to bootand across hardware changes and failures inthe SAN, its called a

persis tentbind. Toestablish a persistent bind, the driver must save this association innonvolatile mem-ory or a configuration file.

Ongoing

MaintenanceOnce the SAN is installed, configured, and doing what you designed

it to do, thingsget much better. Even so, theres still plenty of work to be


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done. The rest of the workinvolves managing, monitoring, and maintainingthe storage.This is the Title of the Book, eMatter EditionCopyright 2011 OReilly & Associates, Inc. All rights reserved.

Ongoing Maintenance|57

Managing (StorageResource Management)Few SANs live on using their initial design. Even the one shown inFigure 3-4can beoutgrown with time. At some point, someone will want to change theSAN in order to:

Increase or decrease the number of servers

If a SAN is successful, it becomes popular. Everybody wants to put theirstorageon the SAN. This results in more HBAs, more ports, and moreswitches. Anothercommon occurrence in SANs is no different than parallel

based SCSI: somebodygets the bright idea of consolidating servers.This, of course, changes the designof the SAN.

Increase or decrease the number of storage arraysWhether youre adding more servers to the SAN or not, the need foraddi tionalstorage capacity will inevitably drive you to purchase more


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storage. Will you buyadditional storage arrays of the size you areusing, or will you look at larger,more centralized storage arrays?Even if you dont grow your storage dramati -cal ly, what ab out

central izing al l your s torage into one or more large

s to ra ge arrays anyway? What affect will these changes have on thenumber of ports andswitches required for your SAN?

Increase or decrease the number of switches, hubs, or routersThis change, of course, i s dr iven by the previous two

ch an ge s. Whet he r yo u increase or decrease the number of serversor storage arrays, it will change thenumber of ports that you need.

Will you buy additional switches and use inter-switch links, orISLs? As you gain experience with your SAN, you will probablyalso

want to increase its level of availability. What about purchasing a

directorclass switch? What does the SAN look like now that youve changedit?You will find yourself asking such questions as you spend more time with

your SAN.The process of asking and answering these questions isnow referred to as

storageresourcemanagement


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(SRM), and there are a number of SRM products now on themark et .Due to the volat i l i ty of this market , I dont l i s t the vendo rshe re , bu t an updated list of SRM products is available at

http://www.storagemountain.com

. How-ever, heres a list of features that are beginning to be typical withSRM products:

Automatic discoveryInstead of having to enter the hundreds of devices that reside on your SAN,theseproducts can automatically query what devices exist on yourSAN. This is anincredible time saver!

Graphical and command line interfacesAlthough being able to view the SAN graphically is one of the best

features ofSRM products, its also helpful to be able to administer things

via the commandline. Many of the products allow you to use all their featuresvia a command lineor graphical interface.This is the Title of the Book, eMatter EditionCopyright 2011 OReilly & Associates, Inc. All rights reserved.


Status reportingAs will be mentioned in the next section, your SAN must be

monitored. MostSRM products incorporate in-band monitoring into their


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products, allowing youto monitor the status of the devices on your SAN aswell as configure them.

SAN visualizationOnce the SRM product has discovered all the devices on your SAN and

checkedtheir status, it can show you a network map of all thedevices, with each devicetype having an icon of a different color andshape. These drawings resemble thenetwork diagrams networkadministrators have grown used to in LAN-basedproducts.

Storage allocationMany of these products can create and modify zones and

create and modi fy LUN masking properties, allowing you to administerthese attributes from a sin-gle source. Often they allow you to do this even on

heterogeneous hardware.

Storage array configuration (virtualization)Some products have worked with the various storage array vendors, and theyareable to create RAID volumes of various levels on the storagearrays in the SANfrom a central point.Relatively speaking, the storage

resource management industry is in its infancy. Asmentionedpreviously, there are a lot of vendors vying for this open market.


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How-ever, SANs will have fully arrived only when these products aremature.

MonitoringIncluding redundant paths and using multiple levels of RAID keepsa single compo-nent failure from causing you any severe grief, but ifyou dont monitor your SAN,youll never know the componentfailed and wont be able to replace it before thenext component

fails.This attribute of ongoing maintenance has already beenmentioned in the previoussection, and the easiest way tomonito r a SAN is to p urchas e an d in stal l an SRM product. What

if you dont have the budget yet? The easiest answer is to build

yourown out-of-band management system using SNMP.Almost al lswitches and storage arrays include an Ethernet port you can plugintoyour LAN or into a dedicated LAN for reporting purposes. Youcan then monitorthem passively or actively. A passive monitoring system

waits for the switch or arrayto noti fy you of a fai lure via an SNMP trap.An active monitoring system involvescreating your own monitoringapplication that issues SNMP queries against yourswitches and


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arrays.LAN administrators and enterprise management applicationscan come in handyhere . Th ey are use d to thi s ki nd ofmon ito rin g a nd can a ssis t y ou in ent eri ng the SNMP world,

especially if you arent that familiar with it.You're ReadingaFree PreviewPages 75 to 164 are not shownin this preview.


Configuring a Filer|149

Some implementations let you configure NIS cache behavior, if

applicable.

passwdand

groupNIS tables are used quite often for UID/GID -to-username matching

andfile-access authent icat ion. Caching the most accessed k eys

is therefore a way toimprove NFS/CIFS file-attribute operationsresponse time.

MicrosoftMicrosoft has supported the sharing of computer resources over the

network for along time, starting with peer-to-peer networking, followed bythe concept of a work-group, then domain, and final ly, complete
http://www.scribd.com/doc/15490613/Using-SANs-and-NAS-Help-for-Storage-Administrators


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directory services. Here are some of theis sues yo u wil l fac e whenusing Microsoft s var ious authent icat ion and directory schemes:

Workgroup modeSmall sites may not need the functionality of domains and ACLs and can

config-ure CIFS for workgroup membership. Shares can be accessedusing share pass-wo rd s an d / or us e r au th en t i ca t i on , bu tA C L s c a n t b e s e t o n f i l e s . S o m e implementations allow only

plaintext password authentication in workgroup mode. Implementations

based on Samba can also be configured to use encryptedpasswords inworkgroup mode using the

smbpasswdfile.

NT4 domain mode

Configuring NAS into an NT4 domain requires a working domainwith at leastone live primary domain controller (PDC). If the NAS

box and PDC arent onthe same subnet, the Windows InternetNaming Service (WINS) is needed tohelp the fi ler find the domain

controller. Usually, the filer serves as a memberserver in thedomain. Domain emulators such as Samba and HP-UXAdvancedServer/9000 might have different configuration


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requirements. (One notable dif-ference is the ability of the filer itself toserve as a domain controller).

Windows 2000 Active Directory (AD)While many vendors claim to have full compatibility with Windows 2000

andActive Directory (AD), some can serve only as NT4 memberservers, and thus

Plaintext PasswordsWindows clients can send their passwords in either plaintext or encrypted format.With the

introduction of Windows NT4 Service Pack 3, Microsoft changed the defaultbehavior of all its client operating

systems to disable the use of plaintext passwords. If your CIFS implementation requires you to use plaintext

passwords (usually requiredfor workgroup mode), you can merge Sambas PlainPassword registry files into

yourPCs registry. PlainPassword files can be found in the Samba source tree, in the docs

directory

.This is the Title of the Book, eMatter EditionCopyright 2011 OReilly & Associates, Inc. All rights reserved.

150|Ch apte r6 : Man agi ng NAS

AD cant be changed from mixed-mode to native-mode. AD offers

many newfeatures that are beyond the scope of this chapter, but forfirst-time configura-tions, the most obvious change is the use ofDNS as a service locator instead of WINS. This requires entering correct


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DNS entries for the domain controllers andthe filer prior to the NASinstallation.

User mappingFilers configured to support multiprotocol users need some

mechanism to translatebetween the different security architectures of CIFSand NFS. NFS inherited the Unixpermission scheme, with its UID/GID and

permissions octets for owner, group, andworld. CIFS behaves muchdifferently, with access control entries (ACE) granting ordenying specific

permissions to specific users or groups, each described by asecurityidentifier (SID). Thus a mechanism is needed to translate theUnix UID/GID to anappropriate CIFS SID and vice versa.The common

method for achieving this involves using the only common fieldtheusername. A mechanism that runs on the filer itself (for example, a

daemon or script)can map between the different usernames and theirunderlying UID/GID and SIDs.An organization that has a consistent

naming convention for usernames across allplatforms will enjoy asmoother and simpler operation.


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ApplicationsThe following section describes some applications your new NAS serverwould workwell with.

Home DirectoriesHome directory configurations depend on the number of users needed. Youcan havemultiple volumes and multiple exports and shares for users. Your

aim is to give usersa simple way to access their home directories fromeverywhere in the network. NASfilers have a way of simplifying this for

both NFS and CIFS.NFS automounterNFS automounter can be used to map an export path on the fi ler tosomethingother than the actual mount path. For example, a directoryon the filer called

nas:/home/curtiscan be mapped in automounter maps to


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/u/curtisor

/users/cur-tis. Even if in the future the account called

curtisis moved to directory called

nas: /home2/curtis2, the change needs only to be done in the automounter map.Thechange is transparent and doesnt affect the users scripts or any other

referenceto his home directory;

/u/curtisis still accessible.This is the Title of the Book, eMatter EditionCopyright 2011 OReilly & Associates, Inc. All rights reserved.

Data Migration|151

CIFS special sharing featuresSome filers have special features for this need. The system can automaticallyfor-ward your mapping to

\\server\usernameto any parent directory that contains adirectory named

username


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. When the user tries to map a drive to his home direc-tory, he isautomatically routed to the correct place. An enhancement to this fea-ture

provides the abi l i ty to combine i t wi th user mapping , so that

i t routescorrectly even if the username isnt the same between Unix and

Windows.

EmailSome vendors supply configuration documents describing how to

configure theirdevices so they can store data from specificapplications, such as email. If you wishto do this, consider the followingfactors:

Average file size

Some email applications, such as Netscape Mail, keep each mailmessage in aseparate file. Some, such as

sendmail, keep all of a single users messages in a sin-gle file. Still others, such asMicrosoft Exchange, keep all mail in one database file. How your emailapplication stores email affects the average file size. This, inturn, affects

performance, filesystem configuration, and the backup strategy.


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Heavy read environmentMost email applications create a lot of read activity because data isread mostlyfrom the server. Most filesystems record the access time(called, in Unix,

atime)of files. Doing that in a heavy read system can be costly, as theupdate of accesstime requires a write. This can affect performance-

tuning efforts, because somefilesystems give you the option not to updateaccess time.

Caching issuesAs descr ibed previously, there are many implementat ions of emai l sof tware.Caching of mai l f i les , especially cl ient -s ide

caching, might be a good perfor-mance practiceor a data

corruption disaster. Consult with your vendor when configuring yourNAS caching with email software.

DatabasesConfiguring NAS for a database requires delicate planning and a closer lookat smalldetails. Care must be taken with the location of database files


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and transaction logs,as well as the setup and testing of your backupand recovery system. You must alsoensure that your database vendorsupports NAS-based datafiles.

Data MigrationNow that your fi le r is configured, youre ready to start copying datainto it . If yourdata is currently stored elsewhere, you need to migrate it tothe filer.This is the Title of the Book, eMatter EditionCopyright 2011 OReilly & Associates, Inc. All rights reserved.


Migration fromDistributed Local

Storage to NAS


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Consolidation of local disks distributed on different hosts and, optionally, ondiffer-ent platforms (and thus different filesystemsUFS, VxFS, JFS, and

NTFS, to name af e w ) i s a c o m m o n g o a l f o r N A S

i mp l em en t e r s . T he r e a r e a nu mbe r o f w a ys t o migrate data

to filers, and a few caveats to keep in mind while migrating thedata,such as permissions and soft links.

Migration methods and toolsHere are some tools and techniques that can help with migrating

from local storageto NAS:

Using a local tapeYou can back up the data using a local tape drive and a backupapplication thatis ava ilable on both the sourc e a nd the fi ler .

Th e big gest pro ble m wi th this method is finding a common backup

and recovery application.Migration to remote tape deviceUsing the remote tape

(rmt)facility Unix-based NAS vendors provide, you canactually use aremote tape for the migration. Since theres extra work that needsto be doneto encode the data stream and send it to the remote host handling


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rmt, this process is usually slower than using a local tape device.

rmtalso doesntsupport Windows clients.

Copying data using the networkSince a large data set migration can cause network overload andinterrupt regu-lar network traffic, you might prefer do the migration during

offline hours or ona different network, assigned only for the migration.

Piped dump and restoreIf you migrate data from Unix, you can eliminate the tape driveduring datamigration by directing the output of

dumpto

restore, as shown here:rshsource

"dump 0f - /vol/vol0" | rshdestination

"restore rf -"

tartar(for tape archive) is a common copying tool. Since the native

tar


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utilitythat comes with modern Unix versions often doesnt handlesoft links, useGNU

tar(

gtar) instead. GNU

taris also available for Windows platforms.A typical migration command linewith

taris:tar cf - . | ( cd /target; tar xf - )

cp and xcopy

Some of the easiest methods to use are Unixs cpor Windows

xcopy. Sincethe NAS filer appears as a network drive, you can simply copy thedata overto it. Remember to do this at an appropriate time.This is the Title of the Book, eMatter EditionCopyright 2011 OReilly & Associates, Inc. All rights reserved.

Data Migration|153When using the


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cpcommand, make sure you issue thedoption alongwith theroption. Thed

option tellscp

not to follow symbolic linkswhen copying. Theroption causes a recursive copy.

Migration issuesWhen migrating data to NAS, you must make sure to preserve

permissions and soft links and take full advantage of the fi lers

performance, (that is , as much as you can within the limits of yournetwork).

Migrating permissionsCare must be taken when migrating permissions; not all tools can

transfer thiskind of information (also calledmetadata, o r d ata tha t d esc ribe s d ata ). Make sure the method you use to

transfer the data preserves permissions, including any access controllists.

Migrating soft links (symbolic links)


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Soft links also arent trivial to migrate. CIFS doesnt translatesymbolic links, socopyin g Un ix d ata that con tain s sy mbo liclin ks to a CIF S vol ume cau ses the symbolic links to be copied as

regular text files. Some Unix tools follow sym-bolic links, and thus

copy the target of the links instead of the links themselves.Somebackup applications have options for following symbolic links orbackingthem up as soft links. Soft links also raise another issue.What if a users homedirectory contains a soft l ink to a file that is

now migrated to NAS? It might bethat the path to the new locationis different than it was, and this soft link willbecome stale after themigration. In any case, you should verify that the migrateddata is accessible

as expected, just like the source.

Performance

Since migration consists of copying data, it would probably help to migratedatain para llel and use inc remental copie s. Paralle l ism rai ses

the total migrat ion throughput, and copying incrementally saves downtime.


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Migration Between

FilersIn the current environment of acquisitions and reorganizations, redistributionof databetween direct ories, volume s an d p hysica l d evices is a

co mmo n req ui rem en t fo rmany companies. In addition to the toolsmentioned earlier, there are additional,proprietary tools just for doingmigration of data between filers:*

NDMPcopyNDMPcopy is an extension of the NDMP specification. NDMPcopy

uses theNDMP protoco l for t ransfe rring da ta bet ween t woNDMP data servers . The* This list of tools is far from comprehensive,andit isnt meant as an endorsement of NetworkAppliance orEMC.



servers can be on the same physical host as well as on separate hosts. Theadvan-tage of this approach is that the data flows between the two servers

using a dedi-cated network connection. Apart from full copies, this alsosupports incrementalcopies up to level 2. The smallest unit of transfer


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is a directory. NDMPcopy issupported on Network Appliance filersfor local and interfiler copying and onAuspex filers (called TurboCopy),for internode copying only.Figure 6-1shows NDMPcopys data flow.

Network Appliance SnapMirror

SnapMirror is a mirroring technology that can also be used for datamigrationbetween filers. Recent versions make it possible to migratethe NFS filehandlesthat are used on the source export to the targetand thus maintain the transpar-enc y o f t he mig ra tio n. Rec en t

versions also offer better granularity, allowingmigration of top-level directories in addition to volumes.

EMC Celerra data movers: unmount/mount volumesMoving volumes between data movers that sit on the same Celerra

box can bed one s imply by unmount ing them on one data

mover , then mount ing themagain on another . I f pre-setup wasdo ne so that ev er y vo lu me ha s it s ow n IP address, migration can

occur transparently for the NFS user.

EMC Celerra TimeFinder/FSTimeFinder, EMCs mirroring product, was extended for NAS usagewith thename of TimeFinder/FS. TimeFinder/FS migrates completevolumes from oneSymmetrix storag e syste m to anothe r. Celerra


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vo lumes can be mi rro red to a remote Symmetrix storage system;the mirror can then be split, and the secondvolume mounted and sharedusing the remote Celerra system.

MaintenanceThis section describes some tasks and issues a filer administrator faces in theday-to-day management of a filer. They include the following:Figure6-1.NDMPcopy data f lowPrimary networkSourcefilerNDMPcommandandcontrol hostDestinationfi lerCommanddialogandfile his tor y Commanddialogandfile histo ry

Dedicatednetwo rkd u mp r es t or e


Maintenance|155

System failures Performance monitoring and analysis Network

and storage management Performance tuning User support

Hardware FailureAll hardware is prone to failure. Be prepared with a plan of actionfor each specificpart, whether its a disk, fan, power supply, CPU, or

motherboard. Most vendorssupply field replaceable units (FRUs) for


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parts that are likely to break in the field.Here are parts most prone tofailure:

DiskWhether your system is configured to use RAID 1, 1+0, 4, 5 or any other

specialcombination, single-disk failures are usually repaired byregenerating the con-tent of the failed disk onto a hot spare disk.This can take a few hours, so makesure to include hot spares in yoursystem and replace any failed disks within areasonable amount of time.

Power supplySome systems have different power supplies for the filer head and

the storageshelves. If redundant power cabling is in use, a power supplyfailure wont causethe whole system to go down.

Fan

There are many different kinds of fans in a filer: CPU fans, systemhead fans,storage s helf fans, a nd ch assis fans. Not al l fanfai lu re s are cri ti cal , but some might be. Check with your vendor as tohow fan failures are handled by the sys-tem.

MemoryWhether its main (RAM), cache (also called L2 cache) or NV-

RAM, memoryconsists of memory module s, su ch a s SIMMs or


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DIMMs that are smal l inte-grated ci rcui t boards with m emorychips on them. In some designs, memorycomes on proprietary

boards.

Motherboard/chassis

These parts are mentioned together because few systems aredesigned to allowyou to replace one without the other. This can becritical, as replacing a chassismight take a long time. Also, in somedesigns, a chassis failure may cause a com-plete system malfunction.

CPUIf your system doesnt offer more than one CPU, a CPU failure

results in a sys-tem failure. Care must be taken with CPU replacementsand, in general, its bestThis is the Title of the Book, eMatter EditionCopyright 2011 OReilly & Associates, Inc. All rights reserved.


to let an experienced hardware technician do this. If your system supportsmorethan one CPU, consult your vendor as to how to handle thefailure of a singleCPU.

CardsSCSI cards, Fibre Channel HBAs, and NICs all fall under this

category. Somedesigns allow for card redundancy, such as usingEtherChannel to avoid havinga single NIC failure take down a network


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link, and using multiple channels fromadapters to storage systems toprotect against a single link failure. Other cardscant be redundant bynature, e.g., parallel SCSI cards.

Hardware UpgradesSome systems al low you to upgrade s ingle components , suchas di sk dr iv es an dCPUs, while others require you to upgrade theentire machine at once. Check withyour vendor about which parts

are upgradeable and which arent. (Disk shelves forexample, canusually hold newer drives but only up to a certain size).

Onsite SparesSome vendors sell you lower-priced parts to use as quick onsitespares. Some of themore common parts for this purpose are sparedisks, which are usual ly kept inside the system itself as hot spares.Companies with strict mean time to recovery (MTTR)requirements require

complete spare systems onsite (which are sometimes also usedaspart of a test envi ronment as well ) . Such spare systems


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should be thoroughly tested so that they can be put into productionquickly when required.

Software FailureThere are a few different reasons your software may fail. Here are the mostcommon:System bugs

NAS is designed and programmed by humans, which means it s

prone to bugs.A bug can cause unexpected results for operations,generic unexpected behav-iors (or under certain conditions or loads), andfeature malfunction. Fixes mightbe supplied by software upgrades as

well as

patches, which are small pieces of software that need to be applied to the originalsoftware.

System panicsIf the NAS operating system code encounters an illegal condition (e.g., a Cfunc-tion for reading a disk block is called with an illegal disk block


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to many

number), it delib-erately causes itself to crash and reboot. In most systemsthis step also dumps allmemory contents into a file, often called a

corefile, which can then be sent to thevendors support center for further analysis.You're ReadingaFree PreviewPages 173 to 197 are not shownin this preview.


182|Chapter7: NAS Backup and Recover y

configure the new NDMP tape servers into your backup application

software, andyou are ready to back up.New tape drives can be used inNDMP libraries irrespective of whether servers back-ing up to it havelocal tape device driver support. This occurs because NDMP back-

ups write to a trusted network end point that happens to be theNDMP tape server.However , to work correctly, the NDMP tape

server needs to have local tape devicedriver support for all its devices.

In fact servers with absolutely no tape device driversupport can use NDMPtape libraries.In general, the performance of these libraries isequivalent per data stream to thatobserved on Fibre Channel SANs.That is, backups are often limited by tape band-width, not network

bandwidth. However, the CPU usage per MB transferred is cur-rently higherthan equivalent SAN deployments.The final issue with suchl ibrar ies is the reason they a re included in this sect ion. Since

NDMP implementations vary in quality, you cant simply purchase
http://www.scribd.com/doc/15490613/Using-SANs-and-NAS-Help-for-Storage-Administratorshttp://www.scribd.com/doc/15490613/Using-SANs-and-NAS-Help-for-Storage-Administrators


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an NDMPagent and automatically assume that you can back up andrecover to and from anyNDMP-capable device. Backup softwarevendors therefore certify whether or not aparticular NDMP

implementation is supported or not. If an NDMP library soundslike it

might fit your needs, make sure your backup software supports it.Filer to server support

Not everyone wants to back up their f i lers v ia a f i le r orNDMP-compat ible tape library. Some would like to simpli fy

matters by simply backing up all their filers totheir Unix or NTbackup server. This would be known as a fi ler to serverbackup.Unfortunately, some backup software products dont support such

backups.

Direct access restore support

If you have large filers, you may find this feature important. Inorder to understandwhat direct access restore is, you must first

understand how NDMP restores workwithout it. Have you everrecovered a single file from a

tararchive via the commandline? You do so with the following command:$ tar xvfdevice-name filename-to-be-recovered

What happens if the file is at the end of the


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tararchive?

tarreads blindly through thearchive, looking for

filename-to-be-recovered. What you see is a long pause, followedby the display of thefilename. What happens if the file is at the beginning of the

tararchive?

taragain reads blindly through the archive, looking for the file. Itdisplaysthe filename as soon as it finds it, but it continues looking through

the archive until itreaches the end. You see the filename displayed, followedby a long pause. Only afterthe long pause is your command-line prompt

returned. Although youve probablynever noticed, unless you hitCtrl-C after you see the filename displayed, the recov-ery time is

unaffected by the position of the file within the archive. Whetherits atThis is the Title of the Book, eMatter EditionCopyright 2011 OReilly & Associates, Inc . All rights reserved.

What About LAN-Free, Client-Free, and Server-Free Backup?|183

the beginning or the end of the file,


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taralways reads through the entire archive look-ing for the pattern youselected.NDMP without direct access support works the same way. Ifyou have a terabyte-sized volume, and you need one file from that volume,

your backup software blindlyreads through the entire terabyte of data forevery single restore. Direct access restoremitigates this problem byallowing the DMA to load only the tape the file is on andto movedirectly to the location of the file on that tape. The difference this

makeswith large restores cant be overstated. If you have largebackups and need to selec -t ively recover individual fi les, you will

definitely want a DMA that supports directaccess restore. However,keep in mind that additional backup information referredto as file

history must be passed from the data server to the DMA to enable

DAR.Enabling file history results in additional DMA processing andnetwork traffic.


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What About

LAN-Free,

Client-Free,and

Server-FreeBackup?


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Earlier in this book, we discussed three kinds of backup that can beperformed withSANS: LAN- f ree Client-free Server-freeWhetheror not NAS systems can perform the above types of backups depends

onwhether or not you look at the NAS system as storage or as

additional clients of thebackup and recovery system.One way to thinkof NAS filers is to consider them no different than anenterprisearray sharing disk to its clients. Filers provide storage totheir clients, and the onlydifference between a filer and a disk array

is the protocol the filer uses to share itsstorage with its clients.Another way to think of NAS filers is to acknowledge thatthey areactually serversmerely specialized servers. They arent just disk

arrays;they are clients of the backup and recovery system.LAN-freebackup occurs when mult iple backup cl ients share a tape library and

arebacking up their data locally via Fibre Channel. If you think ofthe NAS systems asstorage, LAN-free backup doesnt really apply,

because they are merely disk drives. If you think of them as backup systemclients, however, LAN-free backups do apply, asdiscussed previously in thischapter and illustrated inFigure 7-10.Client-free backups occur when the data

is viewed via another source and then trans-ferred to tape using thatsource, instead of sending the data through the backup cli-ent.


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Therefore, client-free backup can occur with NAS only if youconsider them asstorage. First, you create a snapshot, if its possibleto do so. Then you back up thatThis is the Title of the Book, eMatter EditionCopyright 2011 OReilly & Associates, Inc. All rights reserved.


data to tape without ever going through the client that is using the data. Youdo thisby creating an NFS or CIFS mount to the backup server and backingthat up. This isthe equivalent of mounting a split mirror on a SAN.If youthink of the NAS as clients of the backup and recovery system, then client-freebackups are rare. In order for this to happen, the NAS vendor

needs to allow you toaccess the disks behind their filer (oftenreferred to as a

f i l e r h e a d). You then estab-lish and split an additional mirror of the disks

behind the fi ler head, and mount thismirror to a backup server viathe SAN. Usually the only NAS vendors to allow thisare those thatstarted as SAN vendors and have put a NAS head in front of their stor-age

array. Since the storage array can create additional mirrors, they can performcli-ent-free backups. Also, by employing server-to-server mirroring of atargeted volume(or snapshot) as shown back inFigure 7-2, you can move the

backup-to-tape burdenfrom the source filer and perform a LAN-free backup


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on the destination filer, overallproviding the same benefits as client-freebackups on a SAN.Server-free backups occur when the data moves directlyfrom online storage (disk) tooffline storage (tape) without going

through any servers CPU. In order for this tohappen with NAS, you

can consider them only as storage. Then, when you are per -formingNDMP backups that move the data directly from their storage to tape with-o u t g o i n g t h r o u g h a n y o n e e l s e s C P U , i t s l i k e t h e y r e

p e r f o r m i n g s e r v e r - f r e e backups.However, if you consider a NAS

filer as just another client of the backup and recov-ery system,server-free backups are even more rare than client-free backups.Again,the backup and recovery system needs access to their SAN-

attached disks and usesthe extended copy command to move datadirectly from their disks to tape withoutgoing through any CPU. As

with client-free backups, usually the only NAS vendorsthat allowthis are those that started as SAN vendors and have put a NAS head

infront of their storage array. Since the storage array can use extended copy,it can per-form client-free backups.Therefore, LAN-free, client-free, andserver-free backups of filers are all in the eye of the beholder.


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to many

Database

Backup and

RecoveryPrior to the advent of NAS or SAN, al l enterpr ise- class

databases, and even mo st workgroup-class databases were backed upthe same way. The database vendor cre-ated a backup and recovery API

(e.g., Oracles RMAN), and any backup and recov -ery softwarevendors that wanted to back up their database simply wrote to that

API.When the backup and recovery software wanted to back up adatabase, it called the


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Database Backup and Recovery|185

API, the database sent it one or more streams of data, and thesestreams were writ-ten to tape.*

This method is illustrated in the following eight steps are also shown

inFigure 7-12.

1.

Backup software (e.g., NetWorker, NetBackup) asks its backup agent to backupa database2.

Backup softwares agent (e.g., NetWorker Module for Oracle,NetBackup forOracle) tells database backup API it needs to back updatabase.3.

Database backup agent (e.g., Oracles RMAN) tells the database itsgoing to bebacked up.4.

Database (Oracle) requests data to be backed up from storage.5.

Storage passes data to be backed up to database.6.

Database passes data to be backed up to API.7.


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API passes data to be backed up to backup agent.8.

Backup agent passes data to be backed up to backup software, which backs it

upto tape or disk.The only problem with this method is that it uses a

completely different data paththan most backup and recoveryoptions discussed in this chapter. The data paths of the various options

discussed in this chapter are shown inFigure 7-13.Unfortunately, almostall database backup APIs assume that the data will be passedthroughthe database, which retrieves it from storage just as it does du ringnormaloperations. As you can see fromFigure 7-13, th e on ly dat a

path that involves thedatabase server in any way is the NFS/CIFS

option. This means that, in most cases,you will be forced to use NFSor CIFS as your backup method, because its the only way to pass the

data through the database. This is true even if the filer uses a general-purpose operat ing system and s tandard push -agent software .As you can see inFigure 7-13, the path for push-agent software doesnt

go through the database server,* This sectionuses Legato NetWorker andVeritas NetBackup.There are dozens of other products that per-formsimilar backups of databases.NetWorker andNetBackupwere chosenonlybecause manypeople arefamiliar withthem.This isnt anendorsement of these products.

Figure7-12.Standard database backup methodNetbackupornetworker

Backup server

1Networkerornetbackup forOracle

Database serverR M A N O r a c l e

234Filer

5678NFS/CIFSmount


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and the database server is where the database and database backupAPI softwareresides. Therefore, a filer based on a general-purposeoperating system will be of nohelp in this situation.If you want to back

up your filer via snapshots, native backup utilities, NDMP,oranything other than the NFS/CIFS method, you cant (in mostcases) use standarddatabase backup API software. In some cases, such asOracle, this means you need towrite your own script to shut down thedatabase or put it in backup mode prior toperforming your NAS backup.

In other cases, such as SQL Server, you cant performpoint-in-time recoveryof your database if you dont use the database backup API. Ina few cases,such as Network Appliances backup agent for Exchange, you can

usethe database backup API but will need to buy a customized

backup solution fromyour NAS vendor.I dont want to seem like Imbeing hard on NAS. The issues discussed here are nodifferent thanthose discussed inChapter 4with client- and server-free

backups.Because backups that use NDMP, a filer-based push agent, or

snapshots behave likethe client- and server-free backups discussedinChapter 4, your database must sup-port third-party backup in order for

you to back up filer-based data files using thesemethods. And, if you want


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to perform client- or server-free backups of these datafiles on yourfilers, youre probably going to need a custom solution, and theresagood chance youll need to write it yourself.

BenefitsSummaryTable 7-1summarizes the benefits of the various backup and recoveryoptions forNAS filers.Figure7-13.NAS backup option data pathsBackupsoftwareBackup serverNFS/CIFS backupFilerDatabase

Database serverOther filer Tapelibrary

NDMP filer to serverN a t i v e u t i l i t i e s N D M Pf i l e r t o f i l e r P u s ha g e n t N D M P filer to self NFS/CIFS mount


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Benefits Summary|187Table7-1.NAS backup and recovery options summary

Nativeu t i l i t i e s N F S / C I F S ClientsoftwareNDMP:filerto self NDMP:filertofilerNDMP:filerTo NDMPlibraryNDMP:filertobackupserverI m p a c t o n fi l e servingM e d i u m H i g h M e d i

u m L o w C r e a t e s mediuml o a d o n t w o filers

M e d i u m M e d i u m

Load onbackup serverV e r yl o w H i g h M e d i u m V e r y

l o w V e r y l o w V e r y

l o w M e d i u m

Speed of restoreNo directaccessQuick; nodifferentthan astandardrestore,except forNFS/CIFSloadon LAN andfilerQuick; nodifferentthan astandardrestoreQuick(withDAR)Qu ick (wi th DAR)Quick(withDAR)Quick(withDAR)

CostTimerequired tocreatescriptsNoadditionalcostAdditionalinstance of clientversion of backupsoftwareMustpurchaseNDMPagentMustpurchaseNDMPagentMustpurchaseNDMPagentandlibraryMustpurchaseNDMPagent

AvailabilityM o s t f i l e r s A n y f i l e r F i l e r m u s t use fulloperatingsystemFilerandDMAmustsupportNDMPFiler andDMAmustsupportNDMPFiler andDMAmustsupportNDMPFiler andDMAmustsupportNDMP

Portability of backupsPortable toany clientthat canread nativeutilityPortable toany client of backup andrecoverysystemPortable toany clientof

backupandrecoverysystemL i m i t e d L i m i t e d L i m i t e d L i

m i t e d

Can usedatabasebackup APIsN o Y e s No R a r e l

y (somecustomsolutionsavailable)Rarely(somecustomsolutionsavailable)Rarely(somecustomsolutionsavailable)Rarely(somecustomsolutionsavailable)

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