Manage Ceph Services on Proxmox VE Nodes

From Proxmox VE
Jump to: navigation, search

screenshot/gui-ceph-status.png

Proxmox VE unifies your compute and storage systems, i.e. you can use the same physical nodes within a cluster for both computing (processing VMs and containers) and replicated storage. The traditional silos of compute and storage resources can be wrapped up into a single hyper-converged appliance. Separate storage networks (SANs) and connections via network attached storages (NAS) disappear. With the integration of Ceph, an open source software-defined storage platform, Proxmox VE has the ability to run and manage Ceph storage directly on the hypervisor nodes.

Ceph is a distributed object store and file system designed to provide excellent performance, reliability and scalability.

Some advantages of Ceph on Proxmox VE are:
  • Easy setup and management with CLI and GUI support

  • Thin provisioning

  • Snapshots support

  • Self healing

  • Scalable to the exabyte level

  • Setup pools with different performance and redundancy characteristics

  • Data is replicated, making it fault tolerant

  • Runs on economical commodity hardware

  • No need for hardware RAID controllers

  • Open source

For small to mid sized deployments, it is possible to install a Ceph server for RADOS Block Devices (RBD) directly on your Proxmox VE cluster nodes, see Ceph RADOS Block Devices (RBD). Recent hardware has plenty of CPU power and RAM, so running storage services and VMs on the same node is possible.

To simplify management, we provide pveceph - a tool to install and manage Ceph services on Proxmox VE nodes.

Ceph consists of a couple of Daemons
[Ceph intro http://docs.ceph.com/docs/master/start/intro/]
, for use as a RBD storage:
  • Ceph Monitor (ceph-mon)

  • Ceph Manager (ceph-mgr)

  • Ceph OSD (ceph-osd; Object Storage Daemon)

Tip We recommend to get familiar with the Ceph vocabulary.
[Ceph glossary http://docs.ceph.com/docs/luminous/glossary]

Precondition

To build a Proxmox Ceph Cluster there should be at least three (preferably) identical servers for the setup.

A 10Gb network, exclusively used for Ceph, is recommended. A meshed network setup is also an option if there are no 10Gb switches available, see our wiki article
[Full Mesh Network for Ceph https://pve.proxmox.com/wiki/Full_Mesh_Network_for_Ceph_Server]
.

Check also the recommendations from Ceph’s website.

Avoid RAID

As Ceph handles data object redundancy and multiple parallel writes to disks (OSDs) on its own, using a RAID controller normally doesn’t improve performance or availability. On the contrary, Ceph is designed to handle whole disks on it’s own, without any abstraction in between. RAID controller are not designed for the Ceph use case and may complicate things and sometimes even reduce performance, as their write and caching algorithms may interfere with the ones from Ceph.

Warning Avoid RAID controller, use host bus adapter (HBA) instead.

Installation of Ceph Packages

On each node run the installation script as follows:

pveceph install

This sets up an apt package repository in /etc/apt/sources.list.d/ceph.list and installs the required software.

Creating initial Ceph configuration

screenshot/gui-ceph-config.png

After installation of packages, you need to create an initial Ceph configuration on just one node, based on your network (10.10.10.0/24 in the following example) dedicated for Ceph:

pveceph init --network 10.10.10.0/24

This creates an initial configuration at /etc/pve/ceph.conf. That file is automatically distributed to all Proxmox VE nodes by using pmxcfs. The command also creates a symbolic link from /etc/ceph/ceph.conf pointing to that file. So you can simply run Ceph commands without the need to specify a configuration file.

Creating Ceph Monitors

screenshot/gui-ceph-monitor.png

The Ceph Monitor (MON)
[Ceph Monitor http://docs.ceph.com/docs/luminous/start/intro/]
maintains a master copy of the cluster map. For high availability you need to have at least 3 monitors.

On each node where you want to place a monitor (three monitors are recommended), create it by using the Ceph → Monitor tab in the GUI or run.

pveceph createmon

This will also install the needed Ceph Manager (ceph-mgr) by default. If you do not want to install a manager, specify the -exclude-manager option.

Creating Ceph Manager

The Manager daemon runs alongside the monitors, providing an interface for monitoring the cluster. Since the Ceph luminous release the ceph-mgr
[Ceph Manager http://docs.ceph.com/docs/luminous/mgr/]
daemon is required. During monitor installation the ceph manager will be installed as well.

Note It is recommended to install the Ceph Manager on the monitor nodes. For high availability install more then one manager.
pveceph createmgr

Creating Ceph OSDs

screenshot/gui-ceph-osd-status.png

via GUI or via CLI as follows:

pveceph createosd /dev/sd[X]
Tip We recommend a Ceph cluster size, starting with 12 OSDs, distributed evenly among your, at least three nodes (4 OSDs on each node).

If the disk was used before (eg. ZFS/RAID/OSD), to remove partition table, boot sector and any OSD leftover the following commands should be sufficient.

dd if=/dev/zero of=/dev/sd[X] bs=1M count=200
ceph-disk zap /dev/sd[X]
Warning The above commands will destroy data on the disk!

Ceph Bluestore

Starting with the Ceph Kraken release, a new Ceph OSD storage type was introduced, the so called Bluestore
[Ceph Bluestore http://ceph.com/community/new-luminous-bluestore/]
. This is the default when creating OSDs in Ceph luminous.

pveceph createosd /dev/sd[X]
Note In order to select a disk in the GUI, to be more failsafe, the disk needs to have a GPT
[GPT partition table https://en.wikipedia.org/wiki/GUID_Partition_Table]
partition table. You can create this with gdisk /dev/sd(x). If there is no GPT, you cannot select the disk as DB/WAL.

If you want to use a separate DB/WAL device for your OSDs, you can specify it through the -journal_dev option. The WAL is placed with the DB, if not specified separately.

pveceph createosd /dev/sd[X] -journal_dev /dev/sd[Y]
Note The DB stores BlueStore’s internal metadata and the WAL is BlueStore’s internal journal or write-ahead log. It is recommended to use a fast SSDs or NVRAM for better performance.

Ceph Filestore

Till Ceph luminous, Filestore was used as storage type for Ceph OSDs. It can still be used and might give better performance in small setups, when backed by a NVMe SSD or similar.

pveceph createosd /dev/sd[X] -bluestore 0
Note In order to select a disk in the GUI, the disk needs to have a GPT
[GPT]
partition table. You can create this with gdisk /dev/sd(x). If there is no GPT, you cannot select the disk as journal. Currently the journal size is fixed to 5 GB.

If you want to use a dedicated SSD journal disk:

pveceph createosd /dev/sd[X] -journal_dev /dev/sd[Y] -bluestore 0

Example: Use /dev/sdf as data disk (4TB) and /dev/sdb is the dedicated SSD journal disk.

pveceph createosd /dev/sdf -journal_dev /dev/sdb -bluestore 0

This partitions the disk (data and journal partition), creates filesystems and starts the OSD, afterwards it is running and fully functional.

Note This command refuses to initialize disk when it detects existing data. So if you want to overwrite a disk you should remove existing data first. You can do that using: ceph-disk zap /dev/sd[X]

You can create OSDs containing both journal and data partitions or you can place the journal on a dedicated SSD. Using a SSD journal disk is highly recommended to achieve good performance.

Creating Ceph Pools

screenshot/gui-ceph-pools.png

A pool is a logical group for storing objects. It holds Placement Groups (PG, pg_num), a collection of objects.

When no options are given, we set a default of 128 PGs, a size of 3 replicas and a min_size of 2 replicas for serving objects in a degraded state.

Note The default number of PGs works for 2-5 disks. Ceph throws a HEALTH_WARNING if you have too few or too many PGs in your cluster.

It is advised to calculate the PG number depending on your setup, you can find the formula and the PG calculator
[PG calculator http://ceph.com/pgcalc/]
online. While PGs can be increased later on, they can never be decreased.

You can create pools through command line or on the GUI on each PVE host under Ceph → Pools.

pveceph createpool <name>

If you would like to automatically get also a storage definition for your pool, active the checkbox "Add storages" on the GUI or use the command line option --add_storages on pool creation.

Further information on Ceph pool handling can be found in the Ceph pool operation
[Ceph pool operation http://docs.ceph.com/docs/luminous/rados/operations/pools/]
manual.

Ceph CRUSH & device classes

The foundation of Ceph is its algorithm, Controlled Replication Under Scalable Hashing (CRUSH
[CRUSH https://ceph.com/wp-content/uploads/2016/08/weil-crush-sc06.pdf]
).

CRUSH calculates where to store to and retrieve data from, this has the advantage that no central index service is needed. CRUSH works with a map of OSDs, buckets (device locations) and rulesets (data replication) for pools.

Note Further information can be found in the Ceph documentation, under the section CRUSH map
[CRUSH map http://docs.ceph.com/docs/luminous/rados/operations/crush-map/]
.

This map can be altered to reflect different replication hierarchies. The object replicas can be separated (eg. failure domains), while maintaining the desired distribution.

A common use case is to use different classes of disks for different Ceph pools. For this reason, Ceph introduced the device classes with luminous, to accommodate the need for easy ruleset generation.

The device classes can be seen in the ceph osd tree output. These classes represent their own root bucket, which can be seen with the below command.

ceph osd crush tree --show-shadow

Example output form the above command:

ID  CLASS WEIGHT  TYPE NAME
-16  nvme 2.18307 root default~nvme
-13  nvme 0.72769     host sumi1~nvme
 12  nvme 0.72769         osd.12
-14  nvme 0.72769     host sumi2~nvme
 13  nvme 0.72769         osd.13
-15  nvme 0.72769     host sumi3~nvme
 14  nvme 0.72769         osd.14
 -1       7.70544 root default
 -3       2.56848     host sumi1
 12  nvme 0.72769         osd.12
 -5       2.56848     host sumi2
 13  nvme 0.72769         osd.13
 -7       2.56848     host sumi3
 14  nvme 0.72769         osd.14

To let a pool distribute its objects only on a specific device class, you need to create a ruleset with the specific class first.

ceph osd crush rule create-replicated <rule-name> <root> <failure-domain> <class>

<rule-name>

name of the rule, to connect with a pool (seen in GUI & CLI)

<root>

which crush root it should belong to (default ceph root "default")

<failure-domain>

at which failure-domain the objects should be distributed (usually host)

<class>

what type of OSD backing store to use (eg. nvme, ssd, hdd)

Once the rule is in the CRUSH map, you can tell a pool to use the ruleset.

ceph osd pool set <pool-name> crush_rule <rule-name>
Tip If the pool already contains objects, all of these have to be moved accordingly. Depending on your setup this may introduce a big performance hit on your cluster. As an alternative, you can create a new pool and move disks separately.

Ceph Client

screenshot/gui-ceph-log.png

You can then configure Proxmox VE to use such pools to store VM or Container images. Simply use the GUI too add a new RBD storage (see section Ceph RADOS Block Devices (RBD)).

You also need to copy the keyring to a predefined location for a external Ceph cluster. If Ceph is installed on the Proxmox nodes itself, then this will be done automatically.

Note The file name needs to be <storage_id> + `.keyring - <storage_id> is the expression after rbd: in /etc/pve/storage.cfg which is my-ceph-storage in the following example:
mkdir /etc/pve/priv/ceph
cp /etc/ceph/ceph.client.admin.keyring /etc/pve/priv/ceph/my-ceph-storage.keyring

CephFS

Ceph provides also a filesystem running on top of the same object storage as RADOS block devices do. A Metadata Server (MDS) is used to map the RADOS backed objects to files and directories, allowing to provide a POSIX-compliant replicated filesystem. This allows one to have a clustered highly available shared filesystem in an easy way if ceph is already used. Its Metadata Servers guarantee that files get balanced out over the whole Ceph cluster, this way even high load will not overload a single host, which can be be an issue with traditional shared filesystem approaches, like NFS, for example.

Proxmox VE supports both, using an existing CephFS as storage) to save backups, ISO files or container templates and creating a hyper-converged CephFS itself.

Metadata Server (MDS)

CephFS needs at least one Metadata Server to be configured and running to be able to work. One can simply create one through the Proxmox VE web GUI’s Node -> CephFS panel or on the command line with:

pveceph mds create

Multiple metadata servers can be created in a cluster. But with the default settings only one can be active at any time. If an MDS, or its node, becomes unresponsive (or crashes), another standby MDS will get promoted to active. One can speed up the hand-over between the active and a standby MDS up by using the hotstandby parameter option on create, or if you have already created it you may set/add:

mds standby replay = true

in the ceph.conf respective MDS section. With this enabled, this specific MDS will always poll the active one, so that it can take over faster as it is in a warm' state. But naturally, the active polling will cause some additional performance impact on your system and active `MDS.

Multiple Active MDS

Since Luminous (12.2.x) you can also have multiple active metadata servers running, but this is normally only useful for a high count on parallel clients, as else the MDS seldom is the bottleneck. If you want to set this up please refer to the ceph documentation.
[Configuring multiple active MDS daemons http://docs.ceph.com/docs/mimic/cephfs/multimds/]

Create a CephFS

With Proxmox VE’s CephFS integration into you can create a CephFS easily over the Web GUI, the CLI or an external API interface. Some prerequisites are required for this to work:

Prerequisites for a successful CephFS setup:

After this got all checked and done you can simply create a CephFS through either the Web GUI’s Node -> CephFS panel or the command line tool pveceph, for example with:

pveceph fs create --pg_num 128 --add-storage

This creates a CephFS named ‘'cephfs'' using a pool for its data named `'cephfs_data'' with `128` placement groups and a pool for its metadata named 'cephfs_metadata'' with one quarter of the data pools placement groups (`32). Check the Proxmox VE managed Ceph pool chapter or visit the Ceph documentation for more information regarding a fitting placement group number (pg_num) for your setup
[Ceph Placement Groups http://docs.ceph.com/docs/mimic/rados/operations/placement-groups/]
. Additionally, the `--add-storage’ parameter will add the CephFS to the Proxmox VE storage configuration after it was created successfully.

Destroy CephFS

Warning Destroying a CephFS will render all its data unusable, this cannot be undone!

If you really want to destroy an existing CephFS you first need to stop, or destroy, all metadata server (M̀DS). You can destroy them either over the Web GUI or the command line interface, with:

pveceph mds destroy NAME

on each Proxmox VE node hosting a MDS daemon.

Then, you can remove (destroy) CephFS by issuing a:

ceph rm fs NAME --yes-i-really-mean-it

on a single node hosting Ceph. After this you may want to remove the created data and metadata pools, this can be done either over the Web GUI or the CLI with:

pveceph pool destroy NAME