=================
Ceph Random Stuff
=================

Setting Number of Placement Groups
==================================

The number of placement groups is calculated the following way:

.. code-block:: bash

              (OSDs * 100)
  Total PGs = ------------
               Replicas

The number then is rounded up to the next power of two while honoring the magic number of 100 to 200 Target PGs.

.. code-block:: bash

               Total PGs
  Target PGs = ---------
                 OSDs

Example:

* We have 72 OSDs.
* We use Replica = 3 by default.
* The default number of Total PGs calculates to ( (72 * 100) / 3) ) = 2400
* 2400 rounded up would be 4096.
* Total PGs = 4096 gives Target PGs = 56
* Target PGs = 56 is too low, so we use Total PGs = 8192 which gives Target PGs = 113

.. code-block:: bash

   ceph osd pool set rbd pg_num 8192

Setting Number of Placement Groups for Placement
================================================

By default, the number of placement grups for placement is set to the same value
as the number of placement groups.

.. code-block:: bash

   ceph osd pool set rbd pgp_num 8192

Increase Ceph MDS Cache
=======================

.. code-block:: bash

   # /etc/ceph/ceph.conf

   [mds]
   # The number of inodes to cache, default 100000
   mds_cache_size = 30000000

Increase CephFS Max Files per Directory
=======================================

.. code-block:: bash

  # /etc/ceph/ceph.conf

  [mds]
  # hard limit on the size of directory fragments, default 100000
  mds_bal_fragment_size_max = 10000000

Adjust recovery settings
========================

.. code-block:: bash

  # /etc/ceph/ceph.conf

  osd_max_backfills = 1
  osd_recovery_max_active = 1
  osd_scrub_during_recovery = false
  osd_recovery_op_priority = 1

.. code-block:: bash

  # online changes
  ceph tell osd.* injectargs '--osd_max_backfills=9'

Create Ceph Pool
================

Command to create a new pool:

.. code-block:: bash

   ceph osd pool create ${POOL} pg_num

Assign application to Pool
==========================

.. code-block:: bash

   ceph osd pool application enable ${POOL} rbd
   ceph osd pool application enable ${POOL} cephfs