2019.06.27 Intro to Ceph

1
INTRO TO CEPH
OPEN SOURCE DISTRIBUTED STORAGE
Sage Weil
Ceph Tech Talk - 2019.06.27

2
OPEN SOURCE DISTRIBUTED STORAGE
● What is Ceph
○ and why do we care
● Ceph Architecture
○ RADOS
○ RGW - Object
○ RBD - Block
○ CephFS - File
● Management
● Community and Ecosystem
INTRO TO CEPH

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The buzzwords
● “Software defined storage”
● “Unified storage system”
● “Scalable distributed storage”
● “The future of storage”
● “The Linux of storage”
WHAT IS CEPH?
The substance
● Ceph is open source software
● Runs on commodity hardware
○ Commodity servers
○ IP networks
○ HDDs, SSDs, NVMe, NV-DIMMs, ...
● A single cluster can serve object,
block, and file workloads

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● Freedom to use (free as in beer)
● Freedom to introspect, modify,
and share (free as in speech)
● Freedom from vendor lock-in
● Freedom to innovate
CEPH IS FREE AND OPEN SOURCE

5
● Reliable storage service out of unreliable components
○ No single point of failure
○ Data durability via replication or erasure coding
○ No interruption of service from rolling upgrades, online expansion, etc.
● Favor consistency and correctness over performance
CEPH IS RELIABLE

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● Ceph is elastic storage infrastructure
○ Storage cluster may grow or shrink
○ Add or remove hardware while system is
online and under load
● Scale up with bigger, faster hardware
● Scale out within a single cluster for
capacity and performance
● Federate multiple clusters across
sites with asynchronous replication
and disaster recovery capabilities
CEPH IS SCALABLE

7
CEPH IS A UNIFIED STORAGE SYSTEM
RGW
S3 and Swift
object storage
LIBRADOS
Low-level storage API
RADOS
Reliable, elastic, distributed storage layer with
replication and erasure coding
RBD
Virtual block device
CEPHFS
Distributed network
file system
OBJECT BLOCK FILE

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RADOS
● Reliable Autonomic Distributed Object Storage
○ Common storage layer underpinning object, block, and file services
● Provides low-level data object storage service
○ Reliable and highly available
○ Scalable (on day 1 and day 1000)
○ Manages all replication and/or erasure coding, data placement, rebalancing, repair, etc.
● Strong consistency
○ CP, not AP
● Simplifies design and implementation of higher layers (file, block, object)

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RADOS SOFTWARE COMPONENTS
Monitor
● Central authority for authentication, data placement, policy
● Coordination point for all other cluster components
● Protect critical cluster state with Paxos
● 3-7 per cluster
Manager
● Aggregates real-time metrics (throughput, disk usage, etc.)
● Host for pluggable management functions
● 1 active, 1+ standby per cluster
OSD (Object Storage Daemon)
● Stores data on an HDD or SSD
● Services client IO requests
● Cooperatively peers, replicates, rebalances data
● 10s-1000s per cluster
ceph-mgr
ceph-osd
M
ceph-mon

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SERVER
LEGACY CLIENT/SERVER ARCHITECTURE
VIP
BACKUP
BACKEND BACKEND BACKEND
● Virtual IPs
● Failover pairs
● Gateway nodes
APPLICATION

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CLIENT/CLUSTER ARCHITECTURE
APPLICATION
RADOS CLUSTER
LIBRADOS
M
M M
● Smart request routing
● Flexible network addressing
● Same simple application API

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DATA PLACEMENT
APPLICATION
LIBRADOS DATA OBJECT
??
M
M
M

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LOOKUP VIA A METADATA SERVER?
APPLICATION
LIBRADOS
2
1
DATA OBJECT
???
● Lookup step is slow
● Hard to scale to trillions of objects
M
M
M

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CALCULATED PLACEMENT
APPLICATION
LIBRADOS
2
0
DATA OBJECT
● Get map of cluster layout (num OSDs etc) on startup
● Calculate correct object location based on its name
● Read from or write to appropriate OSD
1
M
M
M

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M
M
M
MAP UPDATES WHEN TOPOLOGY CHANGES
APPLICATION
LIBRADOS
5
3
DATA OBJECT
● Get updated map when topology changes
○ e.g., failed device; added node
● (Re)calculate correct object location
● Read from or write to appropriate OSD
4

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RADOS DATA OBJECTS
● Name
○ 10s of characters
○ e.g., “rbd_header.10171e72d03d”
● Attributes
○ 0 to 10s of attributes
○ 0 to 100s of bytes each
○ e.g., “version=12”
● Byte data
○ 0 to 10s of megabytes
● Key/value data (“omap”)
○ 0 to 10,000s of items
○ 0 to 10,000s of bytes each
● Objects live in named “pools”
A: XYZ
B: 1234
FOO: BAR
M: QWERTY
ZZ: FIN
78 20 61 32
74 72 69 63
68 65 20 34
2e 31 35 2e
30 2d 35 30
2d 67 65 6e
POOL

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? → OBJECTS → POOLS → PGs → OSDs
??? OBJECTS
foo.mpg 1532.000
1532.001
1532.002
1532.003
1532.004
1532.005
...
POOL
POOL 1
bazillions of objects
PiB of data
OSDS
N replicas of each PG
10s of PGs per OSD
PLACEMENT GROUPS
pgid = hash(obj_name) % pg_num
many GiB of data per PG
1.0
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.fff
...

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WHY PLACEMENT GROUPS?
REPLICATE DISKS REPLICATE PGS REPLICATE OBJECTS
A A A
B B
C C C
B
D D D
● Each device is mirrored
● Device sizes must match
● Each PG is mirrored
● PG placement is random
● Each object is mirrored
● Object placement is
random

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REPLICATE DISKS
A A A
B B
C C C
B
D D D
B
● Need an empty spare
device to recover
● Recovery bottlenecked
by single disk throughput
REPLICATE PGS
● New PG replicas placed
on surviving devices
● Recovery proceeds in
parallel, leverages many
devices, and completes
sooner
REPLICATE OBJECTS
● Every device participates
in recovery

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REPLICATE DISKS
A A A
B B
C C C
B
D D D
● Very few triple failures
cause data loss (of an
entire disk)
REPLICATE OBJECTS
● Every triple failure
causes data loss (of some
objects)
REPLICATE PGS
● Some triple failures
cause data loss (of an
entire PG)
PGs balance competing extremes

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“Declustered replica placement”
● More clusters
○ Faster recovery
○ More even data distribution
● Fewer clusters
○ Lower risk of concurrent failures affecting
all replicas
● Placement groups a happy medium
○ No need for spare devices
○ Adjustable balance between durability (in
the face of concurrent failures) and
recovery time
Avoiding concurrent failures
● Separate replicas across failure domains
○ Host, rack, row, datacenter
● Create a hierarchy of storage devices
○ Align hierarchy to physical infrastructure
● Express placement policy in terms
hierarchy
KEEPING DATA SAFE
ROOT
DATA CENTER
ROW
RACK
HOST
OSD

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● Pseudo-random placement algorithm
○ Repeatable, deterministic, calculation
○ Similar to “consistent hashing”
● Inputs:
○ Cluster topology (i.e., the OSD hierarchy)
○ Pool parameters (e.g., replication factor)
○ PG id
● Output: ordered list of OSDs
● Rule-based policy
○ “3 replicas, different racks, only SSDs”
○ “6+2 erasure code shards, 2 per rack,
different hosts, only HDDs”
● Stable mapping
○ Limited data migration on change
● Support for varying device sizes
○ OSDs get PGs proportional to their weight
PLACING PGs WITH CRUSH
PLACEMENT GROUPS OSDS
pgid = hash(obj_name) % pg_num
many GiB of data per PG
1.0
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.fff
N replicas of each PG
10s of PGs per OSD
+
PG ID
...

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● Each RADOS pool must be durable
● Each PG must be durable
● Replication
○ Identical copies of each PG
○ Usually 3x (200% overhead)
○ Fast recovery--read any surviving copy
○ Can vary replication factor at any time
● Erasure coding
○ Each PG “shard” has different slice of data
○ Stripe object across k PG shards
○ Keep addition m shards with per-object
parity/redundancy
○ Usually more like 1.5x (50% overhead)
○ Erasure code algorithm and k+m
parameters set when pool is created
○ Better for large objects that rarely change
REPLICATION AND ERASURE CODING
D
A
T
A
D A T A
D A T A
D A T A
1
2
M Y O B J E C T
M Y O B J E C T
M Y O B J E C T
M
Y
O
B
J
E
C
T
1
2
3
4
REPLICATION ERASURE CODING
Two objects
1.5
1.5
1.5
1.5s0
1.5s1
1.5s2
1.5s3
1.5s4
1.5s5

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SPECIALIZED POOLS
● Pools usually share devices
○ Unless a pool’s CRUSH placement policy spcifies a specific class of device
● Elastic, scalable provisioning
○ Deploy hardware to keep up with demand
● Uniform management of devices
○ Common “day 2” workflows to add, remove, replace devices
○ Common management of storage hardware resources
RADOS CLUSTER
3x SSD POOL EC 8+3 HDD POOL 3x HDD POOL

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RADOS VIRTUALIZES STORAGE
RADOS CLUSTER
3x SSD POOL EC 8+3 HDD POOL 3x HDD POOL
M
M M
“MAGIC”

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PLATFORM FOR HIGH-LEVEL SERVICES
RGW
S3 and Swift
object storage
LIBRADOS
RADOS
RBD
CEPHFS
Distributed network
file system
OBJECT BLOCK FILE

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● S3 and Swift-compatible object storage
○ HTTPS/REST-based API
○ Often combined with load balancer to
provide storage service to public internet
● Users, buckets, objects
○ Data and permissions model is based on a
superset of S3 and Swift APIs
○ ACL-based permissions, enforced by RGW
● RGW objects not same as RADOS objects
○ S3 objects can be very big: GB to TB
○ RGW stripes data across RADOS objects
RGW: RADOS GATEWAY
RGW
LIBRADOS
RGW
LIBRADOS
S3
HTTPS
RADOS CLUSTER

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RGW STORES ITS DATA IN RADOS
RGW
LIBRADOS
S3 PUT
USER + BUCKET INFO POOL
DATA POOL 1
BUCKET INDEX POOL
1
2,5
3
4

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RGW ZONE
RGW ZONE: POOLS + RGW DAEMONS
RGW
LIBRADOS
RGW
LIBRADOS
BUCKET INDEX POOL
DATA POOL (3x)
DATA POOL (8+3 EC POOL)

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RGW FEDERATION AND GEO-REP
RGW
LIBRADOS
BUCKET INDEX POOL
DATA POOL (3x)
RGW
LIBRADOS
BUCKET INDEX POOL
DATA POOL (3x)
● Zones may be different clusters and/or sites
● Global view of users and buckets
ZONE A1 ZONE B1
ZONEGROUP A ZONEGROUP B ZONEGROUP C
RGW
LIBRADOS
BUCKET INDEX POOL
DATA POOL (3x)
RGW
LIBRADOS
BUCKET INDEX POOL
DATA POOL (3x)
● Each bucket placed in a ZoneGroup
● Data replicated between all Zones in a ZoneGroup
ZONE C1 ZONE C2
SSL/TLS INTER-ZONE TRAFFIC

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● Very strong S3 API compatibility
○ https://github.com/ceph/s3-tests
functional test suite
● STS: Security Token Service
○ Framework for interoperating with other
authentication/authorization systems
● Encryption (various ﬂavors of API)
● Compression
● CORS and static website hosting
● Metadata search with ElasticSearch
● Pub/sub event stream
○ Integration with knative serverless
○ Kafka
● Multiple storage classes
○ Map classes to RADOS pools
○ Choose storage for individual objects or
set a bucket policy
● Lifecycle management
○ Bucket policy to automatically move
objects between storage tiers and/or
expire
○ Time-based
● Archive zone
○ Archive and preserve full storage history
OTHER RGW FEATURES

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KVM/QEMU
RBD: RADOS BLOCK DEVICE
● Virtual block device
○ Store disk images in RADOS
○ Stripe data across many objects in a pool
● Storage decoupled from host, hypervisor
○ Analogous to AWS’s EBS
● Client implemented in KVM and Linux
● Integrated with
○ Libvirt
○ OpenStack (Cinder, Nova, Glace)
○ Kubernetes
○ Proxmox, CloudStack, Nebula, …
RADOS CLUSTER
LIBRADOS
LIBRBD
VM
LINUX HOST
KRBD
XFS, EXT4, ...
RBD POOL
VIRTIO-BLK

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SNAPSHOTS AND CLONES
● Snapshots
○ Read-only
○ Associated with individual RBD image
○ Point-in-time consistency
BASE OS
VM A
VM B
VM C
● Clones
○ New, ﬁrst-class image
○ Writeable overlay over an existing snapshot
○ Can be snapshotted, resized, renamed, etc.
● Efﬁcient
○ O(1) creation time
○ Leverage copy-on-write support in RADOS
○ Only consume space when data is changed

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RBD: DATA LAYOUT
. . .
● Image name
● Image size
● Striping parameters
● Snapshot metadata (names etc.)
● Options
● Lock owner
● ...
● Chunk of block device content
● 4 MB by default, but striping is conﬁgurable
● Sparse: objects only created if/when data is written
● Replicated or erasure coded, depending on the pool
HEADER DATA OBJECTS

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LIBRADOS
LIBRBD
. . . . . .
RBD: JOURNALING MODE
. . .
● Recent writes
● Metadata changes
1 2
HEADER DATA OBJECTSWRITE JOURNAL

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RBD MIRRORING
CLUSTER BCLUSTER A
DATA POOL (SSD/HDD) DATA POOL
JOURNAL POOL (SSD)
. . . . . .
LIBRADOS
LIBRBD
RBD-MIRROR
LIBRADOS
LIBRBD
LIBRADOS
LIBRBD
● Asynchronous replication by
mirroring journal
● Point-in-time/crash consistent
copy of image in remote cluster
● Mirrors live data and snapshots
● Full lifecycle (fail-over, fail-back,
re-sync, etc.)
● Conﬁgurable per-image
● Scale-out, HA for rbd-mirror

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OTHER RBD FEATURES
● ‘rbd top’
○ Real-time view of IO activity
● Quotas
○ Enforced at provisioning time
● Namespace isolation
○ Restrict access to a private namespace of
RBD images
● Import and export
○ Full image import/export
○ Incremental diff (between snapshots)
● Trash
○ Keep deleted images around for a bit
before purging
● Linux kernel client
○ ‘rbd map myimage’ → /dev/rbd*
● NBD
○ ‘rbd map -t nbd myimage’ → /dev/nbd*
○ Run latest userspace library
● iSCSI gateway
○ LIO stack + userspace tools to manage
gateway conﬁguration
● librbd
○ Dynamically link with application

42
CEPHFS: CEPH FILE SYSTEM
● Distributed network ﬁle system
○ Files, directories, rename, hard links, etc.
○ Concurrent shared access from many
clients
● Strong consistency and coherent caching
○ Updates from one node visible elsewhere,
immediately
● Scale metadata and data independently
○ Storage capacity and IO throughput scale
with the number of OSDs
○ Namespace (e.g., number of ﬁles) scales
with the number of MDS daemons
RADOS CLUSTER
M
M
M
CLIENT HOST
KCEPHFS
01 10
11 00
10 01
00 11
METADATA
DATA

43
CEPH-MDS: METADATA SERVER
MDS (Metadata Server)
● Manage file system namespace
● Store file system metadata in RADOS objects
○ File and directory metadata (names, inodes)
● Coordinate file access between clients
● Manage client cache consistency, locks, leases
● Not part of the data path
● 1s - 10s active, plus standbys
ceph-mds
ceph-mgr ceph-osd
M
ceph-mon

44
METADATA IS STORED IN RADOS
RADOS CLUSTER
METADATA POOL DATA POOL
CLIENT HOST
KCEPHFS
01 10
11 00
10 01
00 11
METADATA
DATA
DIRECTORIES
METADATA JOURNAL

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SCALABLE NAMESPACE
● Partition hierarchy across MDSs based on
workload
● Fragment huge directories across MDSs
● Clients learn overall partition as they navigate
the namespace
● Subtree partition maintains directory locality
● Arbitrarily scalable by adding more MDSs
mds.a mds.b mds.c mds.d mds.e

46
CEPHFS SNAPSHOTS
● Snapshot any directory
○ Applies to all nested files and directories
○ Granular: avoid “volume” and “subvolume”
restrictions in other file systems
● Point-in-time consistent
○ from perspective of POSIX API at client
○ not client/server boundary
● Easy user interface via file system
● Efficient
○ Fast creation/deletion
○ Snapshots only consume space when
changes are made
$ cd any/cephfs/directory
$ ls
foo bar baz/
$ ls .snap
$ mkdir .snap/my_snapshot
$ ls .snap/
my_snapshot/
$ rm foo
$ ls
bar baz/
$ ls .snap/my_snapshot
foo bar baz/
$ rmdir .snap/my_snapshot
$ ls .snap
$

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● MDS maintains recursive stats across the
ﬁle hierarchy
○ File and directory counts
○ File size (summation)
○ Latest ctime
● Visible via virtual xattrs
● Recursive bytes as directory size
○ If mounted with ‘rbytes’ option
○ Unfortunately this confuses rsync; off by
default
○ Similar to ‘du’, but free
CEPHFS RECURSIVE ACCOUNTING
$ sudo mount -t ceph 10.1.2.10:/ /mnt/ceph
-o name=admin,secretfile=secret,rbytes
$ cd /mnt/ceph/some/random/dir
$ getfattr -d -m - .
# file: .
ceph.dir.entries="3"
ceph.dir.files="2"
ceph.dir.subdirs="1"
ceph.dir.rbytes="512000"
ceph.dir.rctime="1474909482.0924860388"
ceph.dir.rentries="17"
ceph.dir.rfiles="16"
ceph.dir.rsubdirs="1"
$ ls -alh
total 12
drwxr-xr-x 3 sage sage 4.5M Jun 25 11:38 ./
drwxr-xr-x 47 sage sage 12G Jun 25 11:38 ../
-rw-r--r-- 1 sage sage 2M Jun 25 11:38 bar
drwxr-xr-x 2 sage sage 500K Jun 25 11:38 baz/
-rw-r--r-- 1 sage sage 2M Jun 25 11:38 foo

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● Multiple file systems (volumes) per cluster
○ Separate ceph-mds daemons
● xattrs
● File locking (flock and fcntl)
● Quotas
○ On any directory
● Subdirectory mounts + access restrictions
● Multiple storage tiers
○ Directory subtree-based policy
○ Place files in different RADOS pools
○ Adjust file striping strategy
● Lazy IO
○ Optionally relax CephFS-enforced
consistency on per-file basis for HPC
applications
● Linux kernel client
○ e.g., mount -t ceph $monip:/ /ceph
● ceph-fuse
○ For use on non-Linux hosts (e.g., OS X) or
when kernel is out of date
● NFS
○ CephFS plugin for nfs-ganesha FSAL
● CIFS
○ CephFS plugin for Samba VFS
● libcephfs
○ Dynamically link with your application
OTHER CEPHFS FEATURES

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COMPLETE STORAGE PLATFORM
RGW
S3 and Swift
object storage
LIBRADOS
RADOS
RBD
CEPHFS
Distributed network
file system
OBJECT BLOCK FILE

51
INTEGRATED DASHBOARD
Monitoring
● Health
● IO and capacity
utilization
Metrics
● Prometheus
● Grafana
Management
● Conﬁguration
● Provisioning
● Day 2 tasks

52
● Internal health monitoring
○ Error and warning states
○ Alert IDs with documentation, mitigation
steps, etc.
● Integrated conﬁguration management
○ Self-documenting
○ History, rollback, etc.
● Device management
○ Map daemons to raw devices
($vendor_$model_$serial)
○ Scrape device health metrics (e.g. SMART)
○ Predict device life expectancy
○ Optionally preemptively evacuate failing
devices
A FEW OTHER MANAGEMENT FEATURES
● Telemetry
○ Phone home anonymized metrics to Ceph
developers
○ Cluster size, utilization, enabled features
○ Crash reports (version + stack trace)
○ Opt-in, obviously

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● Work in progress...
○ Integrated orchestration API
○ Uniﬁed CLI and GUI experience for day 2 ops
○ Pluggable integrations with deployment tools
(Rook, ansible, …, and bare-bones ssh)
● ceph-deploy
○ Bare-bones CLI-based deployment
○ https://github.com/ceph/ceph-deploy
○ Deprecated...
● ceph-ansible
○ Run Ceph on bare metal
○ https://github.com/ceph/ceph-ansible
● Rook
○ Run Ceph in Kubernetes
○ https://rook.io/
● DeepSea
○ SALT-based deployment tool
○ https://github.com/SUSE/DeepSea
● Puppet
○ https://github.com/openstack/puppet-ceph
INSTALLATION OPTIONS

55
● Ceph is open source software!
○ Mostly LGPL2.1/LGPL3
● We collaborate via
○ GitHub: https://github.com/ceph/ceph
○ https://tracker.ceph.com/
○ E-mail: dev@ceph.io
○ #ceph-devel on irc.oftc.net
● We meet a lot over video chat
○ See schedule at http://ceph.io/contribute
● We publish ready-to-use packages
○ CentOS 7, Ubuntu 18.04
● We work with downstream distributions
○ Debian, SUSE, Ubuntu, Red Hat
OPEN DEVELOPMENT COMMUNITY

56
WE INTEGRATE WITH CLOUD ECOSYSTEMS

57
Ceph Days
● One-day regional event
● ~10 per year
● 50-200 people
● Normally a single track of technical talks
● Mostly user-focused
http://ceph.io/cephdays
Cephalocon
● Two-day global event
● Once per year, in the spring
● 300-1000 people
● Multiple tracks
● Users, developers, vendors
http://ceph.io/cephalocon
CEPH EVENTS

58
● http://ceph.io/
● Twitter: @ceph
● Docs: http://docs.ceph.com/
● Mailing lists: http://lists.ceph.io/
○ ceph-announce@ceph.io → announcements
○ ceph-users@ceph.io → user discussion
○ dev@ceph.io → developer discussion
● IRC: irc.oftc.net
○ #ceph, #ceph-devel
● GitHub: https://github.com/ceph/
● YouTube ‘Ceph’ channel
FOR MORE INFORMATION

59
CEPH FOUNDATION
● Organization of industry members
supporting the Ceph project and
community
● 35 members
○ Vendors
○ Cloud companies
○ Major users
○ Academic and government institutions
● Event planning
● Upstream CI infrastructure
● Community hardware test lab

2019.06.27 Intro to Ceph

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2019.06.27 Intro to Ceph