ceph/doc/cluster-ops/pools.rst

=======
 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 
:Type: Integer
:Required: No

``{pgp-num}``

:Description: The total number of placement groups for placement purposes.
:Type: Integer
:Required: No

When you create a pool, you should consider setting the number of 
placement groups.

.. important:: You cannot change the number of placement groups in a pool
   after you create it. 

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}

	
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).