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doc: Added commentary to configure pg defaults. Clarified size commentary.

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Signed-off-by: John Wilkins <john.wilkins@inktank.com>
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John Wilkins 2013-11-22 15:15:41 -08:00
parent dceaef439d
commit fc5789da01
1 changed files with 22 additions and 12 deletions
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34
doc/rados/operations/pools.rst
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@ -50,6 +50,14 @@ The default pools include:
Create a Pool
=============
Before creating pools, refer to the `Pool, PG and CRUSH Config Reference`_.
Ideally, you should override the default value for the number of placement
groups in you Ceph configuration file, as the default is NOT ideal.
For example::
osd pool default pg num = 100
osd pool default pgp num = 100
To create a pool, execute::
ceph osd pool create {pool-name} {pg-num} [{pgp-num}]
@ -60,7 +68,7 @@ Where:
:Description: The name of the pool. It must be unique.
:Type: String
:Required: Yes
:Required: Yes. Picks up default or Ceph configuration value if not specified.
``{pg-num}``
@ -79,9 +87,10 @@ Where:
for placement group splitting scenarios.
:Type: Integer
:Required: Yes
:Required: Yes. Picks up default or Ceph configuration value if not specified.
: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
@ -230,19 +239,15 @@ 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.
You may execute this command for each pool. **Note:** An object might accept
I/Os in degraded mode with fewer than ``pool size`` replicas. To set a minimum
number of required replicas for I/O, 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.
This ensures that no object in the data pool will receive I/O with fewer than
``min_size`` replicas.
Get the Number of Object Replicas
@ -253,4 +258,9 @@ 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).
By default, ceph Creates one replica of an object (a total of two copies, or
a size of 2).
.. _Pool, PG and CRUSH Config Reference: ../../configuration/pool-pg-config-ref