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EMC CLARiiON Backup Storage Solutions CX Series Backup-to-Disk Guide

Abstract

This white paper describes how to configure the CLARiiON CX600, CX400, and CX200 storage systems with various backup applications for best performance as destinations for backups. It also compares the benefits and performance characteristics of backup-to-disk versus backup-to-tape implementations.

Published 2/3/2003

Engineering White Paper

3/12/2003

EMC CLARiiON Storage Solutions CX Series Backup-to-Disk Guide 2

Copyright © 2003 EMC Corporation. All rights reserved.

EMC believes the information in this publication is accurate as of its publication date. The information is subject to change without notice.

THE INFORMATION IN THIS PUBLICATION IS PROVIDED �AS IS.� EMC CORPORATION MAKES NO REPRESENTATIONS OR WARRANTIES OF ANY KIND WITH RESPECT TO THE INFORMATION IN THIS PUBLICATION, AND SPECIFICALLY DISCLAIMS IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Use, copying, and distribution of any EMC software described in this publication requires an applicable software license.

Part Number C976.1

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Table of Contents

Summary..............................................................................................................4 Introduction .........................................................................................................4 Disk Backup Overview........................................................................................5

Advantages of Backup-to-Disk..................................................................................................... 6 Backup Performance ................................................................................................................ 6 Restore Performance................................................................................................................ 6 Media Reliability and Data Availability...................................................................................... 6 Overall IT Efficiency.................................................................................................................. 6

CLARiiON Backup-to-Disk Performance Factors.............................................7 RAID Types .................................................................................................................................. 7 Factors Affecting I/O Sizes........................................................................................................... 7

File System Block Size ............................................................................................................. 7 Disk-Array Element Size........................................................................................................... 8

CLARiiON Configuration Settings ................................................................................................ 8 Disk Array Cache Settings........................................................................................................ 8 LUNs per RAID Group .............................................................................................................. 8

Recommendations for Disk-Based Backups................................................................................ 9 Windows File System Tuning ................................................................................................... 9 Solaris File System Tuning....................................................................................................... 9

EMC CLARiiON Storage Arrays .......................................................................10 ATA Technology......................................................................................................................... 10

Third-Party Disk-Based Backup Applications ................................................11 CA BrightStor ARCserve and BrightStor Enterprise Backup ..................................................... 11

Device Configuration (Disk-Based) ........................................................................................ 11 CommVault Galaxy .................................................................................................................... 12 LEGATO NetWorker................................................................................................................... 12

File Type Device (Version 6.1.x and 7.0) ............................................................................... 12 Advanced File Type Device (Version 7.0 Only)...................................................................... 12

VERITAS Backup Exec .............................................................................................................. 13 VERITAS NetBackup ................................................................................................................. 13

Backup Performance Analysis and Results ...................................................14 Dataset Description .................................................................................................................... 14 Aggregate Performance ............................................................................................................. 14 CLARiiON Raw Throughput Performance ................................................................................. 15 Testing Environment .................................................................................................................. 15 Overall Backup/Restore Time�It�s Not Just the Speed Advantage.......................................... 16 CLARiiON Storage Array versus Native Tape Drive Performance ............................................ 20 Performance Results.................................................................................................................. 20 Backup and Restore Performance Results ................................................................................ 21

Conclusions.......................................................................................................22 Appendix A: Tape Drive Characteristics.........................................................23

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Summary Storage backup solutions that incorporate backup-to-disk yield significant benefits over traditional backup-to-tape. These benefits include:

• Near-term recovery of mission-critical data • Rapid restore from disk • Greater reliability of the backup medium • Multiple host data streams to disk As a complement to using tape for long-term storage, backup-to-disk is an emerging and powerful solution for near-term recovery of mission-critical data. There are many applications that require frequent retrievals of recently captured data, as well as the pervasive need for backup of business transactions that must be preserved and retrieved quickly and efficiently. Leading-edge customers are using disk as the destination for storage management application output.

New Advanced Technology-Attached (ATA) disk technology offers comparable economics to tape and has the performance benefits of disk. Backup arrays or disk-based backups will not replace tape, but will shift tape into an archival role. With EMC CLARiiON® storage system�s RAID protection, data that is backed up to disk is guaranteed to be readable if a recovery of the data is necessary.

Today, EMC recommends adopting a backup-to-disk solution when performance and data reliability are the customer�s primary concern.

Introduction This technical white paper explains implementing backup-to-disk technology with various backup applications and the many advantages over traditional backup-to-tape.

This document contains information relating to backup applications, and identifies what to expect from EMC CLARiiON storage systems when used as backup destinations. It also compares the performance of CLARiiON storage systems to today�s high-performance tape drives such as SDLT and LTO technologies.

EMC�s CLARiiON Application Solutions Integration and Performance Engineering teams performed tests using specific system configurations. Due to variations in hardware, software, disk layout, compressibility of data, system usage, and other factors, backup rates achieved in some situations may be different than those shown herein. All testing performed by the Applications Solutions Integration and Performance Engineering teams used the most up-to-date backup software available at that time. Other versions of these applications may yield other results.

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Disk Backup Overview Traditionally, backup software was created to write to a tape device. Today, most backup software products also allow writing to disk, which means writing to a disk file in a file system. The file system may be on a Windows, NetWare, or UNIX platform, depending on the backup server. Disk-based RAID configurations enhance data protection beyond what tape can provide.

With the CLARiiON CX series storage systems, backups to disk are to a great extent faster than tape drives when comparing raw throughput performance. Backup and restore time using disk provides customers an advantage over using traditional tape. Disk drives are random access devices and can instantly start to transfer the files, whereas with tape, the tape must be loaded and then accessed, increasing the overall time. File system overhead and tape drives with on-board compression add more time lags.

Under normal backup conditions, I/O will always go to physical disk. Performances are generally characterized by the physical disk rotational speed and seek time together with the file system characteristics. Using a larger file system block size or allocation unit size (cluster size) may improve performance of disk backups by using larger contiguous address space for files because the operating system allocates fewer groups of contiguous sectors CLARiiON disk cache improves overall performance. Results show that running with write cache enabled will provide significantly better performance than when cache is turned off.

The CLARiiON engineering team examined the effects of various CLARiiON settings on physical write and read rates prior to running the tests, so that these settings could be varied during the backup tests.

Benefits of CLARiiON disk-based backups that are discussed in more detail in this white paper include:

• Random-access characteristics of disk versus sequential access for tape • Simultaneous capability to read/write to disk • Multiple host data streams • Disk performance vs. tape performance with compression • Aggregate performance • Raw disk performance

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Advantages of Backup-to-Disk Traditionally, tape has been the backup medium of choice, due to its cost-per-MB advantages compared with disk. However, the economics of disk are changing. ATA disk technology offers comparable economics to tape combined with the advantages of disk. The advantages of using disk over tape with backup solutions can be grouped into four major categories:

• Backup performance • Restore performance • Media reliability and data availability • Overall IT efficiency The following sections summarize these category benefits.

Backup Performance • CLARiiON storage systems are much faster than the new-technology tape drives such as SDLT and

LTO. • Some tape technologies respond to a minimal data stream by �shoe-shining� or excessive positioning.

Disks do not experience this behavior because they are inherently random access.

Restore Performance • Faster recovery time for disk drives over tape and tape drives. The difference can be seconds or

minutes versus hours with tape. • Disks support random and sequential access. Tapes support sequential access only. This enables

faster access of data files, improving overall performance. • If data is on several tape cartridges, the following steps are required to restore data:

1. Each tape must be mounted by the library. Time: Up to a minute per tape. 2. The tape must load. Time: 30 seconds to a few minutes. 3. The tape must be positioned to the desired data. Time: Average access time is a few minutes. 4. The tape must be rewound and unloaded. Time: 30 seconds to a few minutes. 5. Load the next tape and repeat cycle.

• Time to first byte takes milliseconds for disk versus seconds to minutes for tape

Media Reliability and Data Availability • Media-specific errors, including faulty tape media, are reduced. Disk-system RAID protection

prevents data unavailability or data loss in the event of a disk drive failure. • Tape handling is reduced or eliminated. Maintaining the set of tapes from a tape library can be

problematic and requires properly trained personnel.

Overall IT Efficiency • Disk does not require tape handling/positioning and RAID protection makes it inherently more

reliable. There is less need to perform frequent full backups. Fewer backups need to be performed, saving network and CPU load.

• Tape undergoes a technology shift every three years, so a conversion from old to new media must be undertaken at that interval. Disk technology does not go through these types of transitions since the format of the data is not changed as it is with tape technology.

• New larger capacity disk drives reduce floor space requirements compared with equivalent-capacity tape libraries.

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CLARiiON Backup-to-Disk Performance Factors This section describes the specific parameters that can be altered to improve performance of backup-to-disk. EMC varied these to determine recommended settings for best performance when backing up to a disk file. In addition to using backup software to measure CLARiiON performance, EMC also used lower-level tests to measure performance.

Backup solutions that use disk as a backup destination, write sequentially to the disk. The source data (data that is read for backup) can be located anywhere on the source. Backup bandwidth to disk can be directly impacted by the fragmentation of the source or file system. Backup packages write in particular block sizes. EMC tested sequential writes with block sizes of 32, 64, 128, and 256 KB.

Note: EMC did not exhaustively test all the combinations of parameters. The number of permutations would be unrealistic to simulate.

RAID Types CLARiiON storage systems use RAID technology to combine disks into one logical unit (LU) to improve reliability and/or performance. CLARiiON supports five RAID types: RAID 5, RAID 3, RAID 1, RAID 0, RAID 1/0. RAID 0 is a simple stripe, and a single drive failure will result in loss of data. The other RAID types offer high availability and data reliability. The storage system can read and write to multiple disks simultaneously and independently, and allow several read/write heads to work on the same task at once.

EMC recommends RAID 5 RAID groups. It offers excellent read performance and good write performance. Write performance benefits greatly from CLARiiON storage-system caching. RAID 5 configurations are very suitable as disk-backup devices.

RAID 1 devices are limited in terms of storage capacity; therefore, they do not lend themselves to backup-to-disk solutions.

RAID 1/0 devices offer both data availability and storage capacity but at a cost. This RAID configuration requires twice the number of disk drives, which increases the backup storage cost.

RAID 3 devices are designed for bandwidth applications that are characterized as very large I/O, 1 MB in size and larger. Backup I/O sizes are typically smaller than this. A RAID 3 device cannot take advantage of the CLARiiON storage-system cache.

RAID 5 configurations are very suitable as disk-backup devices. Destination backup devices are written to in a sequential pattern. The optimizations in FLARE� for RAID 5 devices are a perfect fit for this type of application. The write requests are written to the write cache on the storage system and mirrored in the second storage processor write cache. FLARE then destages this data to disk in an MR3 manner.

Factors Affecting I/O Sizes The following factors affect I/O sizes: • File system block size • Disk-array element size The following sections describe these factors.

File System Block Size Operating systems allocate space for files in blocks. The file system block size varies depending on the OS being used. A larger file system block size provides a large I/O size, which can increase the bandwidth of a backup. Larger block sizes may also help to hinder file system fragmentation. The fragmentation of a file system can also impact the backup bandwidth. The source file system (the file system being read for backup) should be as defragmented as possible. This helps the backup utility to perform read requests more sequentially.

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The default file system block size for UFS, the native Solaris file system, is 8 KB. UFS can be configured with either 4 KB or 8 KB. EMC recommends that the defaults be used.

Disk-Array Element Size The element size of a RAID device is defined as some number of 512-byte sectors. The element size defines the RAID group's stripe size, and this can have an impact on the behavior and therefore performance of a RAID device.

The default element size for a RAID 5 device is 128, which is the 64 KB. A five-drive RAID device has a stripe size of 256 KB. Algorithms in FLARE try to optimize back-end writes to a RAID 5 device. This type of optimized back-end I/O is termed MR3 writes.

EMC recommends using the default RAID 5 element size for devices that will be used for backup-to-disk devices.

CLARiiON Configuration Settings This section describes the CLARiiON-specific parameters that can be altered to improve backup-to-disk performance.

Disk Array Cache Settings CLARiiON storage-system caching improves read and write performance for several types of RAID groups. Read and write caching improve performance in two ways:

• For a read request, the array senses sequential reads from the host, and then starts to prefetch data from the back end into the read cache. The host then reads the data from cache.

• For a write request: � Incoming host write requests are written to cache and then mirrored to the second storage

processor. The host request is then acknowledged. Writing the data to the cache allows for a faster response time.

� If the request modifies the same page in the write cache that has not yet been written to disk, the storage system updates the information in the cache before writing it to disk.

One might anticipate that turning off the CLARiiON storage-system cache would benefit backups. However, EMC found a counter-intuitive result: Performance with the cache off was reduced, even when the writes were aligned on the proper boundaries (such as 256 KB). EMC found minor effects on performance when varying the amount of memory dedicated to write cache. Similarly, little impact was noticed when varying the high and low watermarks.

LUNs per RAID Group EMC recommends only using one LUN per RAID group for disk-based backup applications. Multiple LUNs are not recommended because concurrent I/O would cause the underlying physical disks to seek between the sectors used by the various LUNs, thereby deteriorating performance.

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Recommendations for Disk-Based Backups Consider the following disk-based backup guidelines when planning your CLARiiON configuration:

• Use a five-disk RAID 5 configuration. • Use write cache. In some circumstances, having the write cache enabled will allow misaligned data to

be written out as a hardware stripe (written as MR3). • RAID 10 will give better performance than RAID 5 if boundaries are aligned.

Windows File System Tuning Windows systems create a 63-sector hidden area on disk to house the Master Boot Record (MBR). This causes all I/O in the file system made on the subsequent partition to be misaligned (not on a 256 KB boundary), and therefore I/O performance will suffer. By using a program called diskpar, available on the Windows 2000 Resource Kit, you can alter the number of hidden blocks to a larger number so that the disk array I/Os are aligned and better optimized.

NOTE: The disk defrag tool included in Windows 2000 will not work with cluster sizes greater than the default cluster size of 4 KB.

Solaris File System Tuning There are two possible values to tune with Solaris. The first is to ensure that maxcontig for the file system in question is set high enough; otherwise, rotational delays will be incurred when laying down all the sectors in the write. Set maxcontig to the maximum number of sectors in a write. Since it may be difficult to know exactly what the backup software will use, EMC suggest setting maxcontig to 256 (equivalent to 128 KB since there are 512 bytes in a sector). The maxcontig value may be set when making a file system (such as with newfs) or later with tunefs.

A second value that may be tuned is the maximum number of bytes that can be sent out in a single I/O. This value is by default 128 KB or 256 KB, depending on the hardware on which Solaris is running. There is little reason to go to 256 KB because the backup software would have to change to take advantage of the larger I/O size. For completeness this line may be added to allow 1 MB I/O:

set maxphys=1048576

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EMC CLARiiON Storage Arrays CLARiiON storage systems provide leading performance and investment protection. These storage solutions feature modular building blocks, based on advanced sixth-generation Fibre Channel technology. EMC Fibre Channel CX series disk-array storage systems provide terabytes of disk storage capacity, high transfer rates, flexible configurations, and highly available data at affordable price points. Hardware RAID features are provided two storage processors (SPs). There are three members of the CX series storage-system family: CX600, CX400, and CX200.

Figure 1. CLARiiON CX Series Overview

ATA Technology EMC CLARiiON storage arrays take advantage of ATA disk technology. This technology has the benefits of online disk with the economics of tape. This combination enables customers to keep more data online for longer periods of time. For many, previous alternatives were not affordable or justifiable. CLARiiON storage arrays have incorporated the option of using ATA drives in the array. Customers can mix and match performance Fibre Channel drives and capacity ATA drives within the same array, under common management. The CLARiiON software suite supports ATA drives. This single-array implementation provides the deployment flexibility customers seek.

To optimize CLARiiON storage systems for a backup-to-disk configuration, follow the guidelines in Table 1.

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Table 1. CLARiiON Disk-Based Configuration Guidelines

*Cache values are in MB

Third-Party Disk-Based Backup Applications A number of software backup packages were tested for their ability to back up to disk. Following is a brief description of each one.

CA BrightStor ARCserve and BrightStor Enterprise Backup Computer Associates (CA) BrightStor ARCserve and BrightStor Enterprise Backup are two backup software products that support disk-based backups. The use of the SAN (storage area network) for backup of data on EMC CLARiiON storage systems allows LAN (local area network) resources to be freed, increasing the backup and recovery performance. Additionally, tape libraries and tape drives can be shared among many hosts, each running different operating systems.

EMC CLARiiON storage systems enhance the backup solution with their feature set. Backup and recovery solutions are more reliable and efficient by using features such as high availability, scalability, sharing capabilities, redundancy, and ease of upgrades.

A wide variety of industry-standard components are used with BrightStor ARCserve and BrightStor Enterprise Backup on EMC CLARiiON storage systems in a SAN environment. Each component is thoroughly tested within a SAN environment to ensure their reliability and interoperability. This extensive qualification assures customers that their backup solution will work.

Device Configuration (Disk-Based) Both CA BrightStor ARCserve and Enterprise Backup incorporate disk backup as file system devices. You must first configure file system devices in ARCserve�s Device Configuration GUI or in BrightStor Enterprise Backup GUI in order to write to a disk file. Each file system device is a Windows folder that you specify. A Device Group may include a number of file system devices. Backup will migrate to another file system device when one is full.

CLARiiON Page Read Cache Write Watermark

System Size SP-A SP-B Cache Low High

CX600 16 KB 1,024 1,024 2,048 40 60

CX400 16 KB 50 50 423 40 80

CX200 16 KB 10 10 127 40 80

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CommVault Galaxy CommVault Galaxy software provides a management infrastructure for managing, safeguarding, and recovering your mission-critical data. One feature is their Magnetic Disk as Backup media, which allows customers to add magnetic disk to their backup hierarchy, providing an additional media choice for fast backup and restore.

CommVault incorporates a construct called a magnetic library. It is not an optical disk library. Rather, it is a virtual library with one or more mount paths. A mount path is a disk file system such as a Windows volume or a UNIX mount point. Through the use of this software construct, Galaxy will back up to disk. If more than one disk path is defined for the magnetic library, Galaxy will fill the first disk path, and then span to another disk path. In this way, Galaxy works with disk in a manner similar to how it works with tape.

You can make an auxiliary copy of a backup on a magnetic library. The auxiliary copy can be on tape for archival storage of the backup. When restoring, you may specify which copy to restore from and, therefore, restores can be done directly from the auxiliary copy.

LEGATO NetWorker LEGATO NetWorker supports backups to a disk device that NetWorker calls a file device. NetWorker�s use for the file device is similar to a tape drive, in that it writes a backup container called a saveset to the file device; so, a restore involves unpacking the data held in the saveset. Further, it is possible to write multiple concurrent backups to the same file device, and to have multiple file devices. The LEGATO NetWorker disk backup provides the capability to use a disk device for backup operations. There are two options for disk-to-disk backups:

File Type Device (Version 6.1.x and 7.0) Beginning with release 5.0, NetWorker provided the new device type called file type. The file type device defines the path that will be used to store backup data. The file type device acts very much like a tape device. Data is written to the disk in the same format that is used for tape storage. Multiplexing is permitted, but the output files are not actually multiplexed. Instead, separate files are created for each save set. The maximum amount of space that a file type device will utilize is specified when the device is defined. If the device runs out of space during a backup, then the save sets that are active will span to another device. It is possible to set the size of the device by changing the Default Volume Size value in the advanced options for the device. The name of the device should be the full path to a directory. Like the tape device, it is not possible to simultaneously read and write the device. This of course means that it is not possible to restore from a file type device concurrent with a save operation.

Advanced File Type Device (Version 7.0 Only) In release 7.0, the advanced file type was added to NetWorker. The advanced file type device improves the capabilities of disk backup. With the advanced file type device, it is possible to simultaneously read and write the device. This means that the advanced file type restores can take place even while save operations are in progress. The advanced file type device does not span save sets when the device fills. Instead, the currently active save sets are suspended until space is made available either by deleting old save sets or staging save sets to another device.

NetWorker supports cascading; if a file device fills during backup, NetWorker will automatically continue the backup with another file or other backup device. One possible limitation is that no restores can be done from a particular file device as long as backups are being done to this file device. A best practice is to populate the file device�s Volume Default Capacity field with the amount of disk space that can be used by NetWorker for this volume.

NetWorker also uses a process called staging. Staging copies backup containers (save_sets) from one backup storage medium (usually disk) to another (usually tape). It then removes the save sets from the

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original location. Multiple staging policies can be active simultaneously. Save_sets will be moved/staged based on any or all of the following: age, storage medium percent full, and save set criteria (one of youngest, oldest, largest, and smallest).

VERITAS Backup Exec VERITAS Backup Exec is based on client/server architecture. The backup server must be either a Windows 2000 or Windows NT4 Server. You can have more than one Backup Exec backup server in a SAN configuration. The backup server controls the backup devices it is connected to, including direct-attach and SAN devices.

The Backup Exec clients are any systems containing data to be backed up. A backup server is also a client. UNIX platforms can be Backup Exec clients and are backed up over the LAN. All interaction with Backup Exec, for example submitting jobs, viewing results, and accessing the hardware utility functions, is done through the client. Each backup/restore job is submitted using the Backup Exec client. Administrators can run the client from the backup server or a remote system. After jobs are submitted, the Job Engine on the backup server processes them.

VERITAS BackupExec can back up and restore using disk media including hard drives, NAS appliances, and RAID systems as storage media. Configuring the file system for backups is done through the Device Configuration GUI. Backup-to-Disk Folders are included in the �All Drives� drive pool along with tape devices.

VERITAS NetBackup VERITAS NetBackup is based on a client/server architecture. Each NetBackup client and server belongs to a storage domain. A storage domain consists of a single Master Server, its associated Media Servers, and NetBackup clients. The Master Server controls and directs all NetBackup operations in its storage domain. Each Media Server controls the backup devices it is connected to, including direct-attach and SAN devices. A Media Server can have only one Master Server, but a Master Server can control more than one Media Server. The NetBackup clients are any systems containing data to be backed up. A Master Server can act as a Media Server, and both are capable of being clients.

A NetBackup client is any system with data to be backed up. The client software is tailored to the operating system on which it is installed. Normally, a client operates under the control of the Master Server according to the rules and schedules established by an administrator. A backup client accesses the storage media through a Media Server.

A NetBackup Media Server hosts one or more backup devices (tape or other storage media). Storage devices on the same SAN can be shared between Media Servers using the Shared Storage Option (SSO). The Master Server directs a client to send its data to a Media Server for backup.

A NetBackup Master Server is the manager of the storage domain. An administrator can control all NetBackup functions in the storage domain from the Master Server.

NetBackup manages client data in increments called backup images. A backup image originates from a single client and may consist of a file, a directory, a file system, a partition, or a database. The NetBackup file database on the Master Server contains detailed information about each backup image such as the filename of each file stored, time of backup, size, permissions, ownership, etc. An entry for each backup image is also written in the Master Server's volume database, which maps the backup images to the volumes where they are stored, stores the browse and retention policies for each save set, and maintains tracking information for all storage volumes. The file database and volume database are essential to NetBackup�s ability to locate and recover data rapidly.

To configure VERITAS NetBackup to write to disk, you must set up a disk storage unit. A storage unit is NetBackup�s construct for a collection of like tape drives or, in the case of disk, a container to hold the backup data, a directory on disk. NetBackup allows an unlimited number of disk storage units. However, you must ensure that your backup will not use up the entire disk. If it does, NetBackup will fail. It will not automatically move to another disk storage unit.

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Backup Performance Analysis and Results Customers who are considering moving to a backup-to-disk implementation are usually meeting their backup windows today. To be effective, backup-to-disk needs to be comparable to tape backup in all operational aspects including performance, overall completion time, and reliability. However, the adoption of backup-to-disk will not be driven by improvements in backup performance alone. The combination of affordable price points with the improved performance and reliability create a compelling business proposition.

A subset or single file restored from disk will provide a sizeable improvement compared to restoring the file from tape. Disk-based implementation is the random-access characteristic of a disk drive when performing a restore task. With tape-based backups you must also account for the library media load time, tape ready, seek time, etc. These tasks can add several minutes to hours, in most cases, to the overall time it takes to complete the backup depending on the size of the restore operation.

The following charts show the various backup and restore results for the combinations of CLARiiON storage systems, tape drives, and configuration environments that were tested. In most cases, the Y-axis shows megabytes per second (MB/s) and the X-axis shows the file set used to backup and restore, unless otherwise denoted.

Dataset Description • Large dataset (each directory is 2 GB) � 1 GB size files�2 files � 100 MB size files�20 files � 10 MB size files� 200 files � 1 MB size files� 2,000 files

• Small dataset (directory is 503 MB) � 50 KB size files� 0,000 files

Each CLARiiON storage system was configured with three RAID groups (RAID groups 0 to 2). RAID group 0 was placed on SP-A, and RAID groups 1 and 2 were placed on SP-B, all in a RAID 5 configuration. RAID groups 0 and 1 (FC disks) were configured with five disks, RAID group 2 (serial-ATA disks) were configured with nine disks. In a Microsoft Windows system, each LUN had its own drive letter. On Sun Solaris, there was a mount point for each one.

Each of the dataset files had a representative 2:1 compression ratio. If there were no impediments reading the data from disk, and if the backup software were very efficient writing to the destination device, throughputs to the tape devices would be double the native transfer rate. That implies backup rates of 22 MB/s to SDLT 220, 30 MB/s to LTO, and 32 MB/s to SDLT320 (since the native or uncompressed transfer rates are 11, 15, and 16 MB/s, respectively).

Compressibility of data does not effect the rate at which backups can be done to disk; only tape drives have internal hardware compression. When data cannot be compressed, tape drives would be limited to their native transfer rates. Some file types that are already compressed include video and music files, pictures, zip files, and some database applications, to name just a few. In these scenarios, backup-to-disk performance compares even more favorably to tape than it does with compressible data.

Aggregate Performance Total aggregate performance will vary depending on the type of CLARiiON storage system used, the type of backup host, file system, and nature of the data. Expect a maximum per LUN throughput of 40 to 60 MB/s when only one or two LUNs are active. As more and more backup streams (LUNs) become active, the total aggregate throughput will increase.

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CLARiiON Raw Throughput Performance The CLARiiON storage arrays were tested for raw performance in read and copy operations. The purpose of the read test was to see how fast the data could be read from one LUN. The copy operation tested the CLARiiON storage array for how fast it can read data from one LUN and write it to another LUN on separate RAID groups (and SPs). The following chart shows the results of these tests with the CX600, CX400, and CX200 storage arrays using both Fibre Channel disks (five disk) and serial-ATA disks (nine disk).

68

55

66

45

66

44 4337 37 35

0

10

20

30

40

50

60

70

MB

/Sec

Read Copy

CLARiiON Raw Performance Throughput

CX600 FC

CX600 ATA

CX400 FC

CX400 ATA

CX200 FC

Figure 2. CLARiiON Raw Performance Throughput Results

Testing Environment CX200 CX400 CX600

CrossRoads 10KFC to SCSI Bridge

Tape drive

Tape drive

Tape drive

SDLT 320

SDLT 220

HP LTO

DellPV-132T

IBM LTO

Dell PE-2550W indows 2000

EMC DS-16B2FC Switches

InternalFC Bridge

Sun SolarisEnterprise 250

Figure 3. Backup-to-Disk SAN Testing Configuration Diagram

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Overall Backup/Restore Time�It�s Not Just the Speed Advantage When comparing the performance of a backup-to-disk implementation to a backup-to-tape implementation, you must consider not just the throughput but also the overall time it takes to complete a backup or restore. This section explains the vast difference in overall time it takes to perform a backup or restore task.

In a backup scenario comparing backing up to disk versus backing up to tape, different steps are required to accomplish the job (2 GB in size). A brief description of each task is described along with the average time to complete. In a backup-to-disk scenario, the following steps are involved:

• Upon request, data starts to be transferred from the source (disk) to the destination (disk) (typically less than five seconds depending on backup application to start the transfer).

• Once the dataset has been backed up, the backup application can immediately start the next task.

Disk-to-Disk Backup TimeTotal Elapsed Time :55

4%

96%

File Access Time Xfer Data

Figure 4. Overall Disk-to-Disk Backup Time The advantage of disk-based backups is the random access characteristic of disk drives along with their speed and (in the case of the CLARiiON storage arrays) data protections with RAID protection and redundancy protection.

The overall time it took to back up a 2 GB dataset to disk was 55 seconds; the backup to tape took 3 minutes, 50 seconds.

In a backup-to-tape scenario, the following example illustrates the steps involved:

1. Load a tape cartridge into a tape drive (10 seconds).

2. Wait for the drive to load the tape and become ready (15 seconds; up to 1 minute or more for a new tape media).

3. Tape drive must position the media to where the data will be written (up to 70 seconds or more).

4. Back up the data to tape (performance is determined by a variety of factors)1.

The data could need more than one tape media to complete the backup.

1 Having a fast tape drive doesn�t ensure the highest throughput. If the transfer rate of a tape drive is faster than the host data rate, the tape must stop and reposition frequently, degrading performance.

2 GB Dataset

3/12/2003


5. Unload tape from drive (up to 70 seconds depending on position of tape).

6. Repeat the cycle for each tape that is required.

Disk-to-Tape Backup TimeTotal Elapsed Time 3:50

4% 7% 31%

28%

30%

Tape Load Tape Ready File Access Time Xfer Data Rewind/Unload

Figure 5. Overall Disk-to-Tape Backup Time Only 28 percent of the overall time is actually transferring data to tape; the other 72 percent is tape mechanical movement, file access time, and other tasks. There is extensive overhead associated with backup to tape.

Most applications will stop a backup job if a restore job is submitted. This means unloading the tape in the drive and loading the restore tape. When the restore job is finished, the backup job will continue. With disk-based configurations, both jobs can be running simultaneously.

This section explains differences in overall time to perform a restore of a typical dataset in a backup-to-disk scenario versus a tape restore. This example illustrates a typical scenario where a full backup was performed on one day followed by daily incremental backup, and a subset of the data is to be restored.

In a disk-to-disk restore scenario, the following steps are performed:

1. Upon request, data starts to be restored from the full backup set to the destination site (typically less than five seconds depending on backup application).

2. Once the full dataset has been restored, the first incremental dataset starts to restore, in most cases immediately.

3. The second incremental dataset starts once the first incremental dataset is completed.

4. Data is restored with no additional overhead time, as is the case with tape.

2 GB Dataset

3/12/2003


Disk-to-Disk Restore TimeTotal Elapsed Time :45

4%

96%

File Access Time Xfer Data

Figure 6. Overall Disk-to-Disk Restore Time In the tape restore scenario, the following steps are needed to restore the data that is scattered on several tapes:

1. Load the full backup tape into the drive (10 seconds).

2. Allow time for the drive to load the tape and become ready (15 seconds).

3. Wait for the tape drive to position the media to where the data resides (up to 70 seconds or more).

4. Restore the data to disk (performance is determined by a variety of factors)2.

The data could be on more than one tape and that will add to more overhead time.

5. Unload tape from drive (up to 70 seconds depending on position of tape).

6. Load the first incremental tape into a drive (up to 10 seconds).

7. Wait for the drive to load the tape and become ready (15 seconds).

8. Allow the tape drive to seek to where the data resides (up to 70 seconds or more).

9. Restore the data to disk2.

10. Unload tape from drive (up to 70 seconds).

11. Load the second incremental tape into a drive (10 seconds).

12. Wait for the drive to load the tape and become ready (15 seconds).

13. Allow the tape drive to seek to where the data resides (up to 70 seconds or more).

14. Restore the data to disk.

2 Performance of any tape device with hardware compression depends on the compressibility of the data to achieve maximum performance of the tape drive; otherwise, performance will suffer.

1.5 GB DatasetFull Backup +

Two Incremental

3/12/2003


Data is restored.

If files to be restored are not sequential on tape, you will need to add more time for file seeks on the tape media.

Tape-to-Disk Restore TimeTotal Elapsed Time 12:45

4% 6%

45%

8%

37%

Tape Load Tape Ready File Access Time Xfer Data Rewind/Unload

Figure 7. Overall Tape-to-Disk Restore Time These examples show a typical scenario where a subset of data is requested for restoration. As the chart shows, it took the disk-to-disk restore about 45 seconds to restore the data (1.5 GB). In the tape-to-disk scenario, it took roughly 12 minutes, 45 seconds to complete. This example also accounts for the fact that the requested data can be located on several incremental backup sets or media that must be loaded and unloaded. Users should account for this overhead when comparing performance of restore media.

Customers should consider their recovery time objective, reliability needs, and footprint requirements when determining their optimal solution.

1.5 GB Data SetFull Backup +

Two Incremental

3/12/2003


CLARiiON Storage Array versus Native Tape Drive Performance The following chart shows performance results of all the backup applications tested while backing up a dataset that is either already compressed or where the tape drives have compression turned off.

41 3936

34 34

16 1511

0

10

20

30

40

MB

/Sec

CLARiiON vs. Tape Drive Performance1:1 Data Compression

CX600 FC

CX600 ATA

CX400 FC

CX400 ATA

CX200 FC

SDLT 320

LTOs

SDLT 220

Figure 8. CLARiiON Disk Performance versus Native Tape Results The CLARiiON storage arrays perform two to four times faster than tape drives when the dataset is not compressible or tape drive hardware compression is turned off.

Tape drives can compress data in hardware and achieve better performance. Backup software packages have the ability to compress through software. EMC found that performance suffered significantly when enabling this option, and EMC does not recommend using software compression unless customers are trying to conserve disk space.

Performance Results The following charts compare the performance of backing up to disk versus backing up to tape. The charts only show raw throughput of each device while data is being transferred, and do not take into account tape positioning, file seek times, or library mechanical load/unload times. The dataset shown has a 2:1 data compression rate.

3/12/2003


Backup and Restore Performance Results The following chart shows performance results of all the backup applications tested while backing up a dataset that is either already compressed or where the tape drives have compression turned off.

4136

30

3934

3028

19

0

10

20

30

40

MB

/Sec

Disk-to-DiskFC-to-FC

Disk-to-DiskFC-to-ATA

D-to-TapeFC-to-Tape

Overall Average Backup Performance Data

CX600CX400CX200SDLT320LTOSDLT220

Figure 9. Backup Performance Results

403636 37

33

2725

19

0

10

20

30

40

MB

/Sec

Disk-to-DiskFC-to-FC

Disk-to-DiskFC-to-ATA

D-to-TapeFC-to-Tape

Overall Average Restore Performance Data

CX600CX400CX200SDLT320LTOSDLT220

Figure 10. Restore Performance Results

3/12/2003


Conclusions Backup-to-disk is emerging as a technology that offers significant benefits over the traditional tape backup process. With the changing economics of disk technology, backup-to-disk solutions are now affordable. Leading-edge customers are implementing backup-to-disk solutions as improvements to their existing tape implementations.

All backup applications tested were able to exploit the superior performance of CLARiiON storage systems in backing up to and restoring from disk.

Major advantages of backup-to-disk include:

• Backup performance • Restore performance • Media reliability and data availability • Improved IT Efficiency • Elimination of tape positioning, tape errors, and other mechanical issues • Improved backup reliability • Backup array can be connected to a remote site for data mirrored (disk-to-disk) as a nondisruptive

background IT task Raw Performance Results The following chart shows the CX600 performance percentage gain over the tape drives tested with the large dataset using both FC disks and serial-ATA disks as comparison:

Table 2. CX600 Performance Gain over Tape Drives

Tape Drive Backup Restore

SDLT 320 25% 30% LTO 30% 35% SDLT 220 52% 51%

CX400 and CX200 results, with the SDLT 320, LTO, and SDLT 220 are as follows:

• Backups are up to 13, 19, and 45 percent faster than the tape drives tested • Restores are up to 24, 29, and 46 percent faster Also note the following:

• Disk-based backups can also benefit from using CLARiiON SnapView� point-in-time snapshot capabilities for faster data recovery and efficient business processing.

• Tape will be used more for archival and offsite roles, instead of a front-end data collector. • When configuring a CLARiiON storage system for backups, create an exclusive RAID 5 configuration

with a single LUN per backup server. Multiple systems can share a CLARiiON storage system, with each system having exclusive use of one or more LUNs in the storage array for backup operations.

3/12/2003


Appendix A: Tape Drive Characteristics The following factors affect tape drive performance:

• Media positioning: When a backup or restore is performed, the storage device must position the tape so that the data is over the read/write head. Depending on the location of the data and the overall performance of the media device, this can take a significant amount of time. When you conduct performance analysis with media containing multiple images, it is important to account for the time lag that occurs before the data transfer starts.

• Tape streaming: If a tape device is being used at its most efficient speed, it is said to be streaming the data onto the tape. Generally speaking, if a tape device is streaming, there will be little physical stopping and starting of the media. Instead, the media will be constantly spinning within the tape drive. If the tape device is not being used at its most efficient speed, it may continually start and stop the media from spinning. This behavior is the opposite of tape streaming and usually results in a poor data throughput rate.

• Data compression: Most tape devices support some form of data compression within the tape device itself. Highly compressible data will yield a higher data throughput rate than uncompressible data if the tape device supports hardware data compression. This will be true even if the tape device is able to stream the data onto the tape for both the highly compressible data and the uncompressible data.

• Uncompressible data: If your data is already compressed or is not compressible, then the tape drives will be limited to their native transfer rates. Some file types that are already compressed include video and music files, pictures, zip files, and some database applications, to name just a few.

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