ceph/doc/rados/operations/pools.rst
Josh Durgin 91a0bc891a ceph, rados: update pool delete docs and usage
Signed-off-by: Josh Durgin <josh.durgin@inktank.com>
2013-01-28 16:52:33 -08:00

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=======
Pools
=======
When you first deploy a cluster without creating a pool, Ceph uses the default
pools for storing data. A pool differs from CRUSH's location-based buckets in
that a pool doesn't have a single physical location, and a pool provides you
with some additional functionality, including:
- **Replicas**: You can set the desired number of copies/replicas of an object.
A typical configuration stores an object and one additional copy
(i.e., ``size = 2``), but you can determine the number of copies/replicas.
- **Placement Groups**: You can set the number of placement groups for the pool.
A typical configuration uses approximately 100 placement groups per OSD to
provide optimal balancing without using up too many computing resources. When
setting up multiple pools, be careful to ensure you set a reasonable number of
placement groups for both the pool and the cluster as a whole.
- **CRUSH Rules**: When you store data in a pool, a CRUSH ruleset mapped to the
pool enables CRUSH to identify a rule for the placement of the primary object
and object replicas in your cluster. You can create a custom CRUSH rule for your
pool.
- **Snapshots**: When you create snapshots with ``ceph osd pool mksnap``,
you effectively take a snapshot of a particular pool.
- **Set Ownership**: You can set a user ID as the owner of a pool.
To organize data into pools, you can list, create, and remove pools.
You can also view the utilization statistics for each pool.
List Pools
==========
To list your cluster's pools, execute::
ceph osd lspools
The default pools include:
- ``data``
- ``metadata``
- ``rbd``
.. _createpool:
Create a Pool
=============
To create a pool, execute::
ceph osd pool create {pool-name} {pg-num} [{pgp-num}]
Where:
``{pool-name}``
:Description: The name of the pool. It must be unique.
:Type: String
:Required: Yes
``{pg-num}``
:Description: The total number of placement groups for the pool. See `Placement
Groups`_ for details on calculating a suitable number. The
default value ``8`` is NOT suitable for most systems.
:Type: Integer
:Required: Yes
:Default: 8
``{pgp-num}``
:Description: The total number of placement groups for placement purposes. This
**should be equal to the total number of placement groups**, except
for placement group splitting scenarios.
:Type: Integer
:Required: Yes
:Default: 8
When you create a pool, set the number of placement groups to a reasonable value
(e.g., ``100``). Consider the total number of placement groups per OSD too.
Placement groups are computationally expensive, so performance will degrade when
you have many pools with many placement groups (e.g., 50 pools with 100
placement groups each). The point of diminishing returns depends upon the power
of the OSD host.
.. important:: Increasing the number of placement groups in a pool after you
create the pool is still an experimental feature in Bobtail (v 0.56). We
recommend defining a reasonable number of placement groups and maintaining
that number until Ceph's placement group splitting and merging
functionality matures.
See `Placement Groups`_ for details on calculating an appropriate number of
placement groups for your pool.
.. _Placement Groups: ../placement-groups
Delete a Pool
=============
To delete a pool, execute::
ceph osd pool delete {pool-name} [{pool-name} --yes-i-really-really-mean-it]
If you created your own rulesets and rules for a pool you created, you should
consider removing them when you no longer need your pool. If you created users
with permissions strictly for a pool that no longer exists, you should consider
deleting those users too.
Rename a Pool
=============
To rename a pool, execute::
ceph osd pool rename {current-pool-name} {new-pool-name}
If you rename a pool and you have per-pool capabilities for an authenticated
user, you must update the user's capabilities (i.e., caps) with the new pool
name.
.. note: Version ``0.48`` Argonaut and above.
Show Pool Statistics
====================
To show a pool's utilization statistics, execute::
rados df
Make a Snapshot of a Pool
=========================
To make a snapshot of a pool, execute::
ceph osd pool mksnap {pool-name} {snap-name}
.. note: Version ``0.48`` Argonaut and above.
Remove a Snapshot of a Pool
===========================
To remove a snapshot of a pool, execute::
ceph osd pool rmsnap {pool-name} {snap-name}
.. note: Version ``0.48`` Argonaut and above.
.. _setpoolvalues:
Set Pool Values
===============
To set a value to a pool, execute the following::
ceph osd pool set {pool-name} {key} {value}
You may set values for the following keys:
``size``
:Description: Sets the number of replicas for objects in the pool. See `Set the Number of Object Replicas`_ for further details.
:Type: Integer
``min_size``
:Description: Sets the minimum number of replicas required for io. See `Set the Number of Object Replicas`_ for further details
:Type: Integer
.. note: Version ``0.54`` and above
``crash_replay_interval``
:Description: The number of seconds to allow clients to replay acknowledged, but uncommitted requests.
:Type: Integer
``pgp_num``
:Description: The effective number of placement groups to use when calculating data placement.
:Type: Integer
:Valid Range: Equal to or less than ``pg_num``.
``crush_ruleset``
:Description: The ruleset to use for mapping object placement in the cluster.
:Type: Integer
.. note: Version ``0.48`` Argonaut and above.
Get Pool Values
===============
To set a value to a pool, execute the following::
ceph osd pool get {pool-name} {key}
``pg_num``
:Description: The number of placement groups for the pool.
:Type: Integer
``pgp_num``
:Description: The effective number of placement groups to use when calculating data placement.
:Type: Integer
:Valid Range: Equal to or less than ``pg_num``.
Set the Number of Object Replicas
=================================
To set the number of object replicas, execute the following::
ceph osd pool set {poolname} size {num-replicas}
.. important: The ``{num-replicas}`` includes the object itself.
If you want the object and two copies of the object for a total of
three instances of the object, specify ``3``.
For example::
ceph osd pool set data size 3
You may execute this command for each pool.
Note, however, that pool size is more of a best-effort setting: an object
might accept ios in degraded mode with fewer than size replicas. To
set a minimum number of required replicas for io, you should use the
min_size setting.
For example::
ceph osd pool set data min_size 2
This ensures that no object in the data pool will receive io with fewer than
min_size replicas.
Get the Number of Object Replicas
=================================
To get the number of object replicas, execute the following::
ceph osd dump | grep 'rep size'
Ceph will list the pools, with the ``rep size`` attribute highlighted.
By default, Ceph creates two replicas of an object (two copies).