.. cic1603143369680
.. _config-and-management-ceph-placement-group-number-dimensioning-for-storage-cluster:
============================================================
Ceph Placement Group Number Dimensioning for Storage Cluster
============================================================
Ceph pools are created automatically by |prod-long|, |prod-long| applications,
or by |prod-long| supported optional applications. By default, no
pools are created after the Ceph cluster is provisioned (monitor\(s) enabled
and |OSDs| defined) until it is created by an application or the Rados Gateway
\(RADOS GW) is configured.
The following is a list of pools created by |prod-os|, and Rados Gateway applications.
.. _config-and-management-ceph-placement-group-number-dimensioning-for-storage-cluster-table-gvc-3h5-jnb:
.. table:: Table 1. List of Pools
:widths: auto
+----------------------------------+---------------------+---------------------------------------------------------------+----------+----------------------------------------------------------------------------------------+
| Service/Application | Pool Name | Role | PG Count | Created |
+==================================+=====================+===============================================================+==========+========================================================================================+
| Platform Integration Application | kube-rbd | Kubernetes RBD provisioned PVCs | 64 | When the platform automatically upload/applies after the Ceph cluster is provisioned |
+----------------------------------+---------------------+---------------------------------------------------------------+----------+----------------------------------------------------------------------------------------+
| OpenStack | images | - glance image file storage | 256 | When the user applies the application for the first time |
| | | | | |
| | | - used for VM boot disk images | | |
+----------------------------------+---------------------+---------------------------------------------------------------+----------+----------------------------------------------------------------------------------------+
| | ephemeral | - ephemeral object storage | 256 | |
| | | | | |
| | | - used for VM ephemeral disks | | |
+----------------------------------+---------------------+---------------------------------------------------------------+----------+----------------------------------------------------------------------------------------+
| | cinder-volumes | - persistent block storage | 512 | |
| | | | | |
| | | - used for VM boot disk volumes | | |
| | | | | |
| | | - used as additional disk volumes for VMs booted from images| | |
| | | | | |
| | | - snapshots and persistent backups for volumes | | |
+----------------------------------+---------------------+---------------------------------------------------------------+----------+----------------------------------------------------------------------------------------+
| | cinder.backups | backup cinder volumes | 256 | |
+----------------------------------+---------------------+---------------------------------------------------------------+----------+----------------------------------------------------------------------------------------+
| Rados Gateway | rgw.root | Ceph Object Gateway data | 64 | When the user enables the RADOS GW through the :command:`system service-parameter` CLI |
+----------------------------------+---------------------+---------------------------------------------------------------+----------+----------------------------------------------------------------------------------------+
| | default.rgw.control | Ceph Object Gateway control | 64 | |
+----------------------------------+---------------------+---------------------------------------------------------------+----------+----------------------------------------------------------------------------------------+
| | default.rgw.meta | Ceph Object Gateway metadata | 64 | |
+----------------------------------+---------------------+---------------------------------------------------------------+----------+----------------------------------------------------------------------------------------+
| | default.rgw.log | Ceph Object Gateway log | 64 | |
+----------------------------------+---------------------+---------------------------------------------------------------+----------+----------------------------------------------------------------------------------------+
.. note::
Considering PG value/|OSD| has to be less than 2048 PGs, the default PG
values are calculated based on a setup with one storage replication group
and up to 5 |OSDs| per node.
.. _config-and-management-ceph-placement-group-number-dimensioning-for-storage-cluster-section-vkx-qmt-jnb:
---------------
Recommendations
---------------
For more information on how placement group numbers, (pg_num) can be set
based on how many |OSDs| are in the cluster, see, Ceph PGs per pool calculator:
`https://old.ceph.com/pgcalc/ `__.
You must collect the current pool information (replicated size, number of
|OSDs| in the cluster), and enter it into the calculator, calculate placement
group numbers (pg_num) required based on pg_calc algorithm, estimates on
|OSD| growth, and data percentage to balance Ceph as the number of |OSDs|
scales.
When balancing placement groups for each individual pool, consider the following:
.. _config-and-management-ceph-placement-group-number-dimensioning-for-storage-cluster-ul-vmq-g4t-jnb:
- pgs per osd
- pgs per pool
- pools per osd
- replication
- the crush map (Ceph |OSD| tree)
Running the command, :command:`ceph -s`, displays one of the following
**HEALTH_WARN** messages:
.. _config-and-management-ceph-placement-group-number-dimensioning-for-storage-cluster-ul-sdd-v4t-jnb:
- too few pgs per osd
- too few pgs per pool
- too many pgs per osd
Each of the health warning messages requires manual adjustment of placement
groups for individual pools:
.. _config-and-management-ceph-placement-group-number-dimensioning-for-storage-cluster-ul-dny-15t-jnb:
- To list all the pools in the cluster, use the following command,
:command:`ceph osd lspools`.
- To list all the pools with their pg_num values, use the following command,
:command:`ceph osd dump`.
- To get only the pg_num / pgp_num value, use the following command,
:command:`ceph osd get pg_num`.
**Too few PGs per OSD**
Occurs when a new disk is added to the cluster. For more information on how
to add a disk as an |OSD|, see, |stor-doc|: :ref:`Provisioning Storage on a
Storage Host Using the CLI
`.
To fix this warning, the number of placement groups should be increased, using
the following commands:
.. code-block:: none
~(keystone_admin)$ ceph osd pool set pg_num
.. code-block:: none
~(keystone_admin)$ ceph osd pool set pgp_num
.. note::
Increasing pg_num of a pool has to be done in increments of 64/|OSD|,
otherwise, the above commands are rejected. If this happens, decrease the
pg_num number, retry and wait for the cluster to be **HEALTH_OK** before
proceeding to the the next step. Multiple incremental steps may be required
to achieve the targeted values.
**Too few PGs per Pool**
This indicates that the pool has many more objects per PG than average
(too few PGs allocated). This warning is addressed by increasing the
pg_num of that pool, using the following commands:
.. code-block:: none
~(keystone_admin)$ ceph osd pool set pg_num
.. code-block:: none
~(keystone_admin)$ ceph osd pool set pgp_num
.. note::
pgp_num should be equal to pg_num.
Otherwise, Ceph will issue a warning:
.. code-block:: none
~(keystone_admin)$ ceph -s
cluster:
id: 92bfd149-37c2-43aa-8651-eec2b3e36c17
health: HEALTH_WARN
1 pools have pg_num > pgp_num
**Too many PGs / per OSD**
This warning indicates that the maximum number of 300 PGs per |OSD| is
exceeded. The number of PGs cannot be reduced after the pool is created.
Pools that do not contain any data can safely be deleted and then recreated
with a lower number of PGs. Where pools already contain data, the only
solution is to add OSDs to the cluster so that the ratio of PGs per |OSD|
becomes lower.
.. caution::
Pools have to be created with the exact same properties.
To get these properties, use :command:`ceph osd dump`, or use the following commands:
.. code-block:: none
~(keystone_admin)$ ceph osd pool get cinder-volumes crush_rule
crush_rule: storage_tier_ruleset
.. code-block:: none
~(keystone_admin)$ ceph osd pool get cinder-volumes pg_num
pg_num: 512
.. code-block:: none
~(keystone_admin)$ ceph osd pool get cinder-volumes pgp_num
pg_num: 512
Before you delete a pool, use the following properties to recreate the pool;
pg_num, pgp_num, crush_rule.
To delete a pool, use the following command:
.. code-block:: none
~(keystone_admin)$ ceph osd pool delete
To create a pool, use the parameters from ceph osd dump, and run the following command:
.. code-block:: none
~(keystone_admin)$ ceph osd pool create {pool-name}{pg-num} {pgp-num} {replicated}