ceph: Expand the Precondition section

[pve-docs.git] / pveceph.adoc

[[chapter_pveceph]]
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pveceph(1)
==========
:pve-toplevel:

NAME
----

pveceph - Manage Ceph Services on Proxmox VE Nodes

SYNOPSIS
--------

include::pveceph.1-synopsis.adoc[]

DESCRIPTION
-----------
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Manage Ceph Services on Proxmox VE Nodes
========================================
:pve-toplevel:
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[thumbnail="screenshot/gui-ceph-status.png"]

{pve} 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, {pve} 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 {pve} 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 {pve} cluster nodes, see
xref:ceph_rados_block_devices[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 {pve} nodes.

.Ceph consists of a couple of Daemons footnote:[Ceph intro http://docs.ceph.com/docs/luminous/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 highly recommend to get familiar with Ceph's architecture
footnote:[Ceph architecture http://docs.ceph.com/docs/luminous/architecture/]
and vocabulary
footnote:[Ceph glossary http://docs.ceph.com/docs/luminous/glossary].


Precondition
------------

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

Check also the recommendations from
http://docs.ceph.com/docs/luminous/start/hardware-recommendations/[Ceph's website].

.CPU
As higher the core frequency the better, this will reduce latency.  Among other
things, this benefits the services of Ceph, as they can process data faster.
To simplify planning, you should assign a CPU core (or thread) to each Ceph
service to provide enough resources for stable and durable Ceph performance.

.Memory
Especially in a hyper-converged setup, the memory consumption needs to be
carefully monitored. In addition to the intended workload (VM / Container),
Ceph needs enough memory to provide good and stable performance. As a rule of
thumb, for roughly 1TiB of data, 1 GiB of memory will be used by an OSD. With
additionally needed memory for OSD caching.

.Network
We recommend a network bandwidth of at least 10 GbE or more, which is used
exclusively for Ceph. A meshed network setup
footnote:[Full Mesh Network for Ceph {webwiki-url}Full_Mesh_Network_for_Ceph_Server]
is also an option if there are no 10 GbE switches available.

To be explicit about the network, since Ceph is a distributed network storage,
its traffic must be put on its own physical network. The volume of traffic
especially during recovery will interfere with other services on the same
network.

Further, estimate your bandwidth needs. While one HDD might not saturate a 1 Gb
link, a SSD or a NVMe SSD certainly can. Modern NVMe SSDs will even saturate 10
Gb of bandwidth. You also should consider higher bandwidths, as these tend to
come with lower latency.

.Disks
When planning the size of your Ceph cluster, it is important to take the
recovery time into consideration. Especially with small clusters, the recovery
might take long. It is recommended that you use SSDs instead of HDDs in small
setups to reduce recovery time, minimizing the likelihood of a subsequent
failure event during recovery.

In general SSDs will provide more IOPs then spinning disks. This fact and the
higher cost may make a xref:pve_ceph_device_classes[class based] separation of
pools appealing.  Another possibility to speedup OSDs is to use a faster disk
as journal or DB/WAL device, see xref:pve_ceph_osds[creating Ceph OSDs]. If a
faster disk is used for multiple OSDs, a proper balance between OSD and WAL /
DB (or journal) disk must be selected, otherwise the faster disk becomes the
bottleneck for all linked OSDs.

Aside from the disk type, Ceph best performs with an even sized and distributed
amount of disks per node. For example, 4x disks à 500 GB in each node.

.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.

NOTE: Above recommendations should be seen as a rough guidance for choosing
hardware. Therefore, it is still essential to test your setup and monitor
health & performance.


[[pve_ceph_install]]
Installation of Ceph Packages
-----------------------------

On each node run the installation script as follows:

[source,bash]
----
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
-----------------------------------

[thumbnail="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:

[source,bash]
----
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 {pve} nodes by using
xref:chapter_pmxcfs[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.


[[pve_ceph_monitors]]
Creating Ceph Monitors
----------------------

[thumbnail="screenshot/gui-ceph-monitor.png"]

The Ceph Monitor (MON)
footnote:[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.


[source,bash]
----
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.


[[pve_ceph_manager]]
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 footnote:[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.

[source,bash]
----
pveceph createmgr
----


[[pve_ceph_osds]]
Creating Ceph OSDs
------------------

[thumbnail="screenshot/gui-ceph-osd-status.png"]

via GUI or via CLI as follows:

[source,bash]
----
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.

[source,bash]
----
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
footnote:[Ceph Bluestore http://ceph.com/community/new-luminous-bluestore/].
This is the default when creating OSDs in Ceph luminous.

[source,bash]
----
pveceph createosd /dev/sd[X]
----

NOTE: In order to select a disk in the GUI, to be more fail-safe, the disk needs
to have a GPT footnoteref:[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.

[source,bash]
----
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 SSD 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
an NVMe SSD or similar.

[source,bash]
----
pveceph createosd /dev/sd[X] -bluestore 0
----

NOTE: In order to select a disk in the GUI, the disk needs to have a
GPT footnoteref:[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:

[source,bash]
----
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.

[source,bash]
----
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.


[[pve_ceph_pools]]
Creating Ceph Pools
-------------------

[thumbnail="screenshot/gui-ceph-pools.png"]

A pool is a logical group for storing objects. It holds **P**lacement
**G**roups (`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 footnote:[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**.

[source,bash]
----
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 footnote:[Ceph pool operation
http://docs.ceph.com/docs/luminous/rados/operations/pools/]
manual.

[[pve_ceph_device_classes]]
Ceph CRUSH & device classes
---------------------------
The foundation of Ceph is its algorithm, **C**ontrolled **R**eplication
**U**nder **S**calable **H**ashing
(CRUSH footnote:[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 footnote:[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.

[source, bash]
----
ceph osd crush tree --show-shadow
----

Example output form the above command:

[source, bash]
----
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.

[source, bash]
----
ceph osd crush rule create-replicated <rule-name> <root> <failure-domain> <class>
----

[frame="none",grid="none", align="left", cols="30%,70%"]
|===
|<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.

[source, bash]
----
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
-----------

[thumbnail="screenshot/gui-ceph-log.png"]

You can then configure {pve} to use such pools to store VM or
Container images. Simply use the GUI too add a new `RBD` storage (see
section xref:ceph_rados_block_devices[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:

[source,bash]
----
mkdir /etc/pve/priv/ceph
cp /etc/ceph/ceph.client.admin.keyring /etc/pve/priv/ceph/my-ceph-storage.keyring
----

[[pveceph_fs]]
CephFS
------

Ceph provides also a filesystem running on top of the same object storage as
RADOS block devices do. A **M**eta**d**ata **S**erver (`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
an issue with traditional shared filesystem approaches, like `NFS`, for
example.

{pve} supports both, using an existing xref:storage_cephfs[CephFS as storage])
to save backups, ISO files or container templates and creating a
hyper-converged CephFS itself.


[[pveceph_fs_mds]]
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 {pve} 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. footnote:[Configuring multiple active MDS
daemons http://docs.ceph.com/docs/luminous/cephfs/multimds/]

[[pveceph_fs_create]]
Create a CephFS
~~~~~~~~~~~~~~~

With {pve}'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:
- xref:pve_ceph_install[Install Ceph packages], if this was already done some
  time ago you might want to rerun it on an up to date system to ensure that
  also all CephFS related packages get installed.
- xref:pve_ceph_monitors[Setup Monitors]
- xref:pve_ceph_monitors[Setup your OSDs]
- xref:pveceph_fs_mds[Setup at least one MDS]

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 xref:pve_ceph_pools[{pve} managed Ceph pool chapter] or visit the
Ceph documentation for more information regarding a fitting placement group
number (`pg_num`) for your setup footnote:[Ceph Placement Groups
http://docs.ceph.com/docs/luminous/rados/operations/placement-groups/].
Additionally, the `'--add-storage'' parameter will add the CephFS to the {pve}
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 {pve} node hosting a MDS daemon.

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

----
ceph fs rm 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
----


Ceph monitoring and troubleshooting
-----------------------------------
A good start is to continuosly monitor the ceph health from the start of
initial deployment. Either through the ceph tools itself, but also by accessing
the status through the {pve} link:api-viewer/index.html[API].

The following ceph commands below can be used to see if the cluster is healthy
('HEALTH_OK'), if there are warnings ('HEALTH_WARN'), or even errors
('HEALTH_ERR'). If the cluster is in an unhealthy state the status commands
below will also give you an overview on the current events and actions take.

----
# single time output
pve# ceph -s
# continuously output status changes (press CTRL+C to stop)
pve# ceph -w
----

To get a more detailed view, every ceph service has a log file under
`/var/log/ceph/` and if there is not enough detail, the log level can be
adjusted footnote:[Ceph log and debugging http://docs.ceph.com/docs/luminous/rados/troubleshooting/log-and-debug/].

You can find more information about troubleshooting
footnote:[Ceph troubleshooting http://docs.ceph.com/docs/luminous/rados/troubleshooting/]
a Ceph cluster on its website.


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