Storage Developer Conference - 09/19/2012

2012 Storage Developer Conference. © Inktank. All Rights Reserved.

Ceph: scaling storage for the cloud and beyond

Sage Weil

Inktank


outline● why you should care● what is it, what it does● distributed object storage● ceph fs● who we are, why we do this


why should you care about anotherstorage system?


requirements● diverse storage needs

– object storage

– block devices (for VMs) with snapshots, cloning

– shared file system with POSIX, coherent caches

– structured data... files, block devices, or objects?

● scale– terabytes, petabytes, exabytes

– heterogeneous hardware

– reliability and fault tolerance


time● ease of administration● no manual data migration, load balancing● painless scaling

– expansion and contraction

– seamless migration


cost● linear function of size or performance● incremental expansion

– no fork-lift upgrades

● no vendor lock-in– choice of hardware

– choice of software

● open


what is ceph?


unified storage system● objects

– native

– RESTful

● block– thin provisioning, snapshots, cloning

● file– strong consistency, snapshots


RADOS

A reliable, autonomous, distributed object store comprised of self-healing, self-managing, intelligent storage nodes

RADOS


LIBRADOS

A library allowingapps to directlyaccess RADOS,with support forC, C++, Java,Python, Ruby,and PHP

LIBRADOS


RBD

A reliable and fully-distributed block device, with a Linux kernel client and a QEMU/KVM driver

RBD


CEPH FS

A POSIX-compliant distributed file system, with a Linux kernel client and support for FUSE

CEPH FS


RADOSGW

A bucket-based REST gateway, compatible with S3 and Swift

RADOSGW


APPAPP APPAPP HOST/VMHOST/VM CLIENTCLIENT


open source● LGPLv2

– copyleft

– ok to link to proprietary code

● no copyright assignment– no dual licensing

– no “enterprise-only” feature set

● active community● commercial support


distributed storage system● data center scale

– 10s to 10,000s of machines

– terabytes to exabytes

● fault tolerant– no single point of failure

– commodity hardware

● self-managing, self-healing


ceph object model● pools

– 1s to 100s

– independent namespaces or object collections

– replication level, placement policy

● objects– bazillions

– blob of data (bytes to gigabytes)

– attributes (e.g., “version=12”; bytes to kilobytes)

– key/value bundle (bytes to gigabytes)


why start with objects?● more useful than (disk) blocks

– names in a single flat namespace

– variable size

– simple API with rich semantics

● more scalable than files– no hard-to-distribute hierarchy

– update semantics do not span objects

– workload is trivially parallel


HUMANHUMAN COMPUTERCOMPUTER DISKDISK

DISKDISK

DISKDISK

DISKDISK

DISKDISK

DISKDISK

DISKDISK


HUMANHUMAN COMPUTERCOMPUTER DISKDISK

DISKDISK

DISKDISK

DISKDISK

DISKDISK

DISKDISK

DISKDISK

HUMANHUMAN

HUMANHUMAN


DISKDISK

DISKDISK

DISKDISK

DISKDISK

DISKDISK

DISKDISK

DISKDISK

DISKDISK

DISKDISK

DISKDISK

DISKDISK

DISKDISK

HUMANHUMAN

HUMANHUMAN

HUMANHUMAN

HUMANHUMAN

HUMANHUMAN

HUMANHUMAN

HUMANHUMANHUMANHUMAN


HUMANHUMAN


HUMANHUMAN

HUMANHUMAN

HUMANHUMAN

HUMANHUMAN

HUMANHUMAN

HUMANHUMAN

HUMANHUMAN

HUMANHUMAN

HUMANHUMAN (actually more like this…)

(COMPUTER)(COMPUTER)


DISKDISK

HUMANHUMAN

HUMANHUMAN

HUMANHUMAN

DISKDISK

DISKDISK

DISKDISK

DISKDISK

DISKDISK

DISKDISK

DISKDISK

DISKDISK

DISKDISK

DISKDISK

DISKDISK

COMPUTERCOMPUTER

COMPUTERCOMPUTER

COMPUTERCOMPUTER

COMPUTERCOMPUTER

COMPUTERCOMPUTER

COMPUTERCOMPUTER

COMPUTERCOMPUTER

COMPUTERCOMPUTER

COMPUTERCOMPUTER

COMPUTERCOMPUTER

COMPUTERCOMPUTER

COMPUTERCOMPUTER


DISK

FS

DISK DISK

OSD

DISK DISK

OSD OSD OSD OSD

FS FS FSFS btrfsxfsext4

MMM


Monitors:

• Maintain cluster membership and state

• Provide consensus for distributed decision-making via Paxos

• Small, odd number

• These do not serve stored objects to clients

M

Object Storage Daemons (OSDs):• At least three in a cluster• One per disk or RAID group• Serve stored objects to clients• Intelligently peer to perform

replication tasks


M

M

M

HUMAN


data distribution● all objects are replicated N times● objects are automatically placed, balanced,

migrated in a dynamic cluster● must consider physical infrastructure

– ceph-osds on hosts in racks in rows in data centers

● three approaches– pick a spot; remember where you put it– pick a spot; write down where you put it

– calculate where to put it, where to find it


CRUSH• Pseudo-random placement

algorithm

• Fast calculation, no lookup

• Repeatable, deterministic

• Ensures even distribution

• Stable mapping

• Limited data migration

• Rule-based configuration

• specifiable replication

• infrastructure topology aware

• allows weighting


10 10 01 01 10 10 01 11 01 1010 10 01 01 10 10 01 11 01 10

1010 1010 0101 0101 1010 1010 0101 1111 0101 1010

hash(object name) % num pg

CRUSH(pg, cluster state, policy)


10 10 01 01 10 10 01 11 01 1010 10 01 01 10 10 01 11 01 10

1010 1010 0101 0101 1010 1010 0101 1111 0101 1010


RADOS● monitors publish osd map that describes cluster state

– ceph-osd node status (up/down, weight, IP)

– CRUSH function specifying desired data distribution

● object storage daemons (OSDs)– safely replicate and store object

– migrate data as the cluster changes over time

– coordinate based on shared view of reality – gossip!

● decentralized, distributed approach allows– massive scales (10,000s of servers or more)

– the illusion of a single copy with consistent behavior

M


CLIENTCLIENT

??




CLIENT

??


RADOS


RADOS


LIBRADOS


RBD


RBD


CEPH FS


CEPH FS


RADOSGW


RADOSGW




LIBRADOSLIBRADOS

MM

MM

MM

APPAPP

native


LLLIBRADOS

• Provides direct access to RADOS for applications

• C, C++, Python, PHP, Java• No HTTP overhead


atomic transactions● client operations send to the OSD cluster

– operate on a single object

– can contain a sequence of operations, e.g.● truncate object● write new object data● set attribute

● atomicity– all operations commit or do not commit atomically

● conditional– 'guard' operations can control whether operation is performed

● verify xattr has specific value● assert object is a specific version

– allows atomic compare-and-swap etc.


key/value storage● store key/value pairs in an object

– independent from object attrs or byte data payload

● based on google's leveldb– efficient random and range insert/query/removal

– based on BigTable SSTable design

● exposed via key/value API– insert, update, remove

– individual keys or ranges of keys

● avoid read/modify/write cycle for updating complex objects– e.g., file system directory objects


watch/notify● establish stateful 'watch' on an object

– client interest persistently registered with object

– client keeps session to OSD open

● send 'notify' messages to all watchers– notify message (and payload) is distributed to all watchers

– variable timeout

– notification on completion● all watchers got and acknowledged the notify

● use any object as a communication/synchronization channel– locking, distributed coordination (ala ZooKeeper), etc.


CLIENT #1

CLIENT #2

CLIENT #3

OSD

watch

ack/commit

ack/commit

watch

ack/commitwatch

notify

notify

notify

notify

ackack

ack

complete


watch/notify example● radosgw cache consistency

– radosgw instances watch a single object (.rgw/notify)

– locally cache bucket metadata

– on bucket metadata changes (removal, ACL changes)

● write change to relevant bucket object● send notify with bucket name to other radosgw

instances

– on receipt of notify● invalidate relevant portion of cache


rados classes● dynamically loaded .so

– /var/lib/rados-classes/*

– implement new object “methods” using existing methods

– part of I/O pipeline

– simple internal API

● reads– can call existing native or class methods

– do whatever processing is appropriate

– return data

● writes– can call existing native or class methods

– do whatever processing is appropriate

– generates a resulting transaction to be applied atomically


class examples● grep

– read an object, filter out individual records, and return those

● sha1– read object, generate fingerprint, return that

● images– rotate, resize, crop image stored in object

– remove red-eye

● crypto– encrypt/decrypt object data with provided key


RADOS


RADOS


LIBRADOS


LIBRADOS


RBD


RBD


CEPH FS


CEPH FS


RADOSGW




RADOS


RADOS


LIBRADOS


LIBRADOS


CEPH FS


CEPH FS


RADOSGW


RADOSGW



RBD



DISKDISK

COMPUTERCOMPUTER

DISKDISK

DISKDISK

DISKDISK

DISKDISK

DISKDISK

DISKDISK

DISKDISK

DISKDISK

DISKDISK

DISKDISK

DISKDISK

COMPUTERCOMPUTER

COMPUTERCOMPUTER

COMPUTERCOMPUTER

COMPUTERCOMPUTER

COMPUTERCOMPUTER

COMPUTERCOMPUTER

COMPUTERCOMPUTER

COMPUTERCOMPUTER

COMPUTERCOMPUTER

COMPUTERCOMPUTER

COMPUTERCOMPUTER

COMPUTERCOMPUTER

DISKDISK


DISKDISK

DISKDISK

DISKDISK

DISKDISK

DISKDISK

DISKDISK

DISKDISK

DISKDISK

DISKDISK

DISKDISK

DISKDISK

DISKDISK

COMPUTERCOMPUTER

COMPUTERCOMPUTER

COMPUTERCOMPUTER

COMPUTERCOMPUTER

COMPUTERCOMPUTER

COMPUTERCOMPUTER

COMPUTERCOMPUTER

COMPUTERCOMPUTER

COMPUTERCOMPUTER

COMPUTERCOMPUTER

COMPUTERCOMPUTER

COMPUTERCOMPUTER

VMVM

VMVM

VMVM


RADOS Block Device:• Storage of virtual disks in RADOS• Decouples VMs and containers

• Live migration!• Images are striped across the cluster• Snapshots!• Support in

• Qemu/KVM

• OpenStack, CloudStack

• Mainline Linux kernel

• Image cloning

• Copy-on-write “snapshot” of existing image


MM

MM

MM

VMVM

LIBRADOSLIBRADOS

LIBRBDLIBRBD

VIRTUALIZATION CONTAINERVIRTUALIZATION CONTAINER


LIBRADOSLIBRADOS

MM

MM

MM

LIBRBDLIBRBD

CONTAINERCONTAINER

LIBRADOSLIBRADOS

LIBRBDLIBRBD

CONTAINERCONTAINERVMVM


LIBRADOSLIBRADOS

MM

MM

MM

KRBD (KERNEL MODULE)KRBD (KERNEL MODULE)

HOSTHOST


RADOS


RADOS


LIBRADOS


LIBRADOS


RBD


RBD


CEPH FS


RADOSGW


RADOSGW




MM

MM

MM

CLIENTCLIENT

0110

0110

datametadata


MM

MM

MM


Metadata Server• Manages metadata for a

POSIX-compliant shared filesystem• Directory hierarchy• File metadata (owner,

timestamps, mode, etc.)• Stores metadata in RADOS• Does not serve file data to

clients• Only required for shared

filesystem


legacy metadata storage● a scaling disaster

– name → inode → block list → data

– no inode table locality

– fragmentation● inode table● directory

● many seeks● difficult to partition

usr

etc

var

home

vmlinuz

passwdmtabhosts

lib…

…

…

includebin


ceph fs metadata storage● block lists unnecessary● inode table mostly useless

– APIs are path-based, not inode-based

– no random table access, sloppy caching

● embed inodes inside directories– good locality, prefetching

– leverage key/value object

102

100

1

usr

etc

var

home

vmlinuz

passwdmtabhosts

libincludebin

…

…

…


one tree

three metadata servers

??






DYNAMIC SUBTREE PARTITIONING


● scalable– arbitrarily partition

metadata

● adaptive– move work from busy

to idle servers

– replicate hot metadata

● efficient– hierarchical partition

preserve locality

● dynamic– daemons can

join/leave

– take over for failed nodes

dynamic subtree partitioning


controlling metadata io

journal

directories

● view ceph-mds as cache– reduce reads

● dir+inode prefetching

– reduce writes● consolidate multiple writes

● large journal or log– stripe over objects

– two tiers● journal for short term● per-directory for long term

– fast failure recovery


what is journaled● lots of state

– journaling is expensive up-front, cheap to recover

– non-journaled state is cheap, but complex (and somewhat expensive) to recover

● yes– client sessions

– actual fs metadata modifications

● no– cache provenance

– open files

● lazy flush– client modifications may not be durable until fsync() or visible by

another client


client protocol● highly stateful

– consistent, fine-grained caching

● seamless hand-off between ceph-mds daemons– when client traverses hierarchy

– when metadata is migrated between servers

● direct access to OSDs for file I/O


an example● mount -t ceph 1.2.3.4:/ /mnt

– 3 ceph-mon RT

– 2 ceph-mds RT (1 ceph-mds to -osd RT)

● cd /mnt/foo/bar

– 2 ceph-mds RT (2 ceph-mds to -osd RT)

● ls -al

– open

– readdir

● 1 ceph-mds RT (1 ceph-mds to -osd RT)

– stat each file

– close

● cp * /tmp

– N ceph-osd RT

ceph-mon

ceph-mds

ceph-osd


recursive accounting● ceph-mds tracks recursive directory stats

– file sizes

– file and directory counts

– modification time

● virtual xattrs present full stats● efficient

$ ls alSh | headtotal 0drwxrxrx 1 root root 9.7T 20110204 15:51 .drwxrxrx 1 root root 9.7T 20101216 15:06 ..drwxrxrx 1 pomceph pg4194980 9.6T 20110224 08:25 pomcephdrwxrxrx 1 mcg_test1 pg2419992 23G 20110202 08:57 mcg_test1drwxx 1 luko adm 19G 20110121 12:17 lukodrwxx 1 eest adm 14G 20110204 16:29 eestdrwxrxrx 1 mcg_test2 pg2419992 3.0G 20110202 09:34 mcg_test2drwxx 1 fuzyceph adm 1.5G 20110118 10:46 fuzycephdrwxrxrx 1 dallasceph pg275 596M 20110114 10:06 dallasceph


snapshots● volume or subvolume snapshots unusable at petabyte scale

– snapshot arbitrary subdirectories

● simple interface– hidden '.snap' directory

– no special tools

$ mkdir foo/.snap/one # create snapshot$ ls foo/.snapone$ ls foo/bar/.snap_one_1099511627776 # parent's snap name is mangled$ rm foo/myfile$ ls -F foobar/$ ls -F foo/.snap/onemyfile bar/$ rmdir foo/.snap/one # remove snapshot


multiple client implementations● Linux kernel client

– mount -t ceph 1.2.3.4:/ /mnt

– export (NFS), Samba (CIFS)

● ceph-fuse● libcephfs.so

– your app

– Samba (CIFS)

– Ganesha (NFS)

– Hadoop (map/reduce)

kernel

libcephfs

ceph fuseceph-fuse

your app

libcephfsSamba

libcephfsGanesha

NFS SMB/CIFS

libcephfsHadoop


RADOS


RADOS


LIBRADOS


LIBRADOS


RBD


RBD


RADOSGW


RADOSGW



CEPH FS


CEPH FS


NEARLYAWESOME

AWESOMEAWESOME

AWESOME

AWESOME


why we do this● limited options for scalable open source

storage● proprietary solutions

– expensive

– don't scale (well or out)

– marry hardware and software

● industry ready for change


who we are● Ceph created at UC Santa Cruz (2004-2007)● developed by DreamHost (2008-2011)● supported by Inktank (2012)

– Los Angeles, Sunnyvale, San Francisco, remote

● growing user and developer community– Linux distros, users, cloud stacks, SIs, OEMs


thanks

sage weil

[email protected]

@liewegas http://github.com/ceph

http://ceph.com/

mailto:[email protected]

http://github.com/ceph

http://ceph.com/

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Storage Developer Conference - 09/19/2012

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