ceph/doc/rados/configuration/osd-config-ref.rst

======================
 OSD Config Reference
======================

.. index:: OSD; configuration

You can configure Ceph OSD Daemons in the Ceph configuration file, but Ceph OSD
Daemons can use the default values and a very minimal configuration. A minimal
Ceph OSD Daemon configuration sets ``osd journal size`` and ``osd host``,  and
uses default values for nearly everything else.

Ceph OSD Daemons are numerically identified in incremental fashion, beginning
with ``0`` using the following convention. ::

	osd.0
	osd.1
	osd.2

In a configuration file, you may specify settings for all Ceph OSD Daemons in
the cluster by adding configuration settings to the ``[osd]`` section of your
configuration file. To add settings directly to a specific Ceph OSD Daemon
(e.g., ``osd host``), enter  it in an OSD-specific section of your configuration
file. For example:

.. code-block:: ini
	
	[osd]
		osd journal size = 1024
	
	[osd.0]
		osd host = osd-host-a
		
	[osd.1]
		osd host = osd-host-b


.. index:: OSD; config settings

General Settings
================

The following settings provide an Ceph OSD Daemon's ID, and determine paths to
data and journals. Ceph deployment scripts typically generate the UUID
automatically. We **DO NOT** recommend changing the default paths for data or
journals, as it makes it more problematic to troubleshoot Ceph later. 

The journal size should be at least twice the product of the expected drive
speed multiplied by ``filestore max sync interval``. However, the most common
practice is to partition the journal drive (often an SSD), and mount it such
that Ceph uses the entire partition for the journal.


``osd uuid``

:Description: The universally unique identifier (UUID) for the Ceph OSD Daemon.
:Type: UUID
:Default: The UUID.
:Note: The ``osd uuid`` applies to a single Ceph OSD Daemon. The ``fsid`` 
       applies to the entire cluster.


``osd data`` 

:Description: The path to the OSDs data. You must create the directory when 
              deploying Ceph. You should mount a drive for OSD data at this 
              mount point. We do not recommend changing the default. 

:Type: String
:Default: ``/var/lib/ceph/osd/$cluster-$id``


``osd max write size`` 

:Description: The maximum size of a write in megabytes.
:Type: 32-bit Integer
:Default: ``90``


``osd client message size cap`` 

:Description: The largest client data message allowed in memory.
:Type: 64-bit Integer Unsigned
:Default: 500MB default. ``500*1024L*1024L`` 


``osd class dir`` 

:Description: The class path for RADOS class plug-ins.
:Type: String
:Default: ``$libdir/rados-classes``

.. index:: OSD; journal settings

Journal Settings
================

By default, Ceph expects that you will store an Ceph OSD Daemons journal with
the  following path::

	/var/lib/ceph/osd/$cluster-$id/journal

Without performance optimization, Ceph stores the journal on the same disk as
the Ceph OSD Daemons data. An Ceph OSD Daemon optimized for performance may use
a separate disk to store journal data (e.g., a solid state drive delivers high
performance journaling).

Ceph's default ``osd journal size`` is 0, so you will need to set this in your
``ceph.conf`` file. A journal size should find the product of the ``filestore
max sync interval`` and the expected throughput, and multiply the product by
two (2)::  
	  
	osd journal size = {2 * (expected throughput * filestore max sync interval)}

The expected throughput number should include the expected disk throughput
(i.e., sustained data transfer rate), and network throughput. For example, 
a 7200 RPM disk will likely have approximately 100 MB/s. Taking the ``min()``
of the disk and network throughput should provide a reasonable expected 
throughput. Some users just start off with a 10GB journal size. For 
example::

	osd journal size = 10000


``osd journal`` 

:Description: The path to the OSD's journal. This may be a path to a file or a
              block device (such as a partition of an SSD). If it is a file, 
              you must create the directory to contain it. We recommend using a
              drive separate from the ``osd data`` drive.

:Type: String
:Default: ``/var/lib/ceph/osd/$cluster-$id/journal``


``osd journal size`` 

:Description: The size of the journal in megabytes. If this is 0, and the 
              journal is a block device, the entire block device is used. 
              Since v0.54, this is ignored if the journal is a block device, 
              and the entire block device is used.

:Type: 32-bit Integer
:Default: ``5120``
:Recommended: Begin with 1GB. Should be at least twice the product of the 
              expected speed multiplied by ``filestore max sync interval``.


See `Journal Config Reference`_ for additional details.


Monitor OSD Interaction
=======================

Ceph OSD Daemons check each other's heartbeats and report to monitors
periodically. Ceph can use default values in many cases. However, if your
network  has latency issues, you may need to adopt longer intervals. See
`Configuring Monitor/OSD Interaction`_ for a detailed discussion of heartbeats.


Data Placement
==============

See `Pool & PG Config Reference`_ for details.


.. index:: OSD; scrubbing

Scrubbing
=========

In addition to making multiple copies of objects, Ceph insures data integrity by
scrubbing placement groups. Ceph scrubbing is analogous to ``fsck`` on the
object storage layer. For each placement group, Ceph generates a catalog of all
objects and compares each primary object and its replicas to ensure that no
objects are missing or mismatched. Light scrubbing (daily) checks the object
size and attributes.  Deep scrubbing (weekly) reads the data and uses checksums
to ensure data integrity.

Scrubbing is important for maintaining data integrity, but it can reduce
performance. You can adjust the following settings to increase or decrease
scrubbing operations.


``osd max scrubs`` 

:Description: The maximum number of simultaneous scrub operations for 
              a Ceph OSD Daemon.

:Type: 32-bit Int
:Default: ``1`` 


``osd scrub thread timeout`` 

:Description: The maximum time in seconds before timing out a scrub thread.
:Type: 32-bit Integer
:Default: ``60`` 


``osd scrub finalize thread timeout`` 

:Description: The maximum time in seconds before timing out a scrub finalize 
              thread.

:Type: 32-bit Integer
:Default: ``60*10``


``osd scrub load threshold`` 

:Description: The maximum load. Ceph will not scrub when the system load 
              (as defined by ``getloadavg()``) is higher than this number. 
              Default is ``0.5``.

:Type: Float
:Default: ``0.5`` 


``osd scrub min interval`` 

:Description: The maximum interval in seconds for scrubbing the Ceph OSD Daemon
              when the Ceph Storage Cluster load is low.

:Type: Float
:Default: 5 minutes. ``300`` 


``osd scrub max interval`` 

:Description: The maximum interval in seconds for scrubbing the Ceph OSD Daemon 
              irrespective of cluster load.

:Type: Float
:Default: Once per day. ``60*60*24`` 


``osd deep scrub interval``

:Description: The interval for "deep" scrubbing (fully reading all data).
:Type: Float
:Default: Once per week.  ``60*60*24*7``


``osd deep scrub stride``

:Description: Read size when doing a deep scrub.
:Type: 32-bit Int
:Default: 512 KB. ``524288``


.. index:: OSD; operations settings

Operations
==========

Operations settings allow you to configure the number of threads for servicing
requests. If you set ``osd op threads`` to ``0``, it disables multi-threading.
By default, Ceph  uses two threads with a 30 second timeout and a 30 second
complaint time if an operation doesn't complete within those time parameters.
You can set operations priority weights between client operations and
recovery operations to ensure optimal performance during recovery.


``osd op threads`` 

:Description: The number of threads to service Ceph OSD Daemon operations. 
              Set to ``0`` to disable it. Increasing the number may increase 
              the request processing rate.

:Type: 32-bit Integer
:Default: ``2`` 


``osd client op priority``

:Description: The priority set for client operations. It is relative to 
              ``osd recovery op priority``.

:Type: 32-bit Integer
:Default: ``63`` 
:Valid Range: 1-63


``osd recovery op priority``

:Description: The priority set for recovery operations. It is relative to 
              ``osd client op priority``.

:Type: 32-bit Integer
:Default: ``10`` 
:Valid Range: 1-63


``osd op thread timeout`` 

:Description: The Ceph OSD Daemon operation thread timeout in seconds.
:Type: 32-bit Integer
:Default: ``30`` 


``osd op complaint time`` 

:Description: An operation becomes complaint worthy after the specified number
              of seconds have elapsed.

:Type: Float
:Default: ``30`` 


``osd disk threads`` 

:Description: The number of disk threads, which are used to perform background 
              disk intensive OSD operations such as scrubbing and snap 
              trimming.

:Type: 32-bit Integer
:Default: ``1`` 


``osd op history size``

:Description: The maximum number of completed operations to track.
:Type: 32-bit Unsigned Integer
:Default: ``20``


``osd op history duration``

:Description: The oldest completed operation to track.
:Type: 32-bit Unsigned Integer
:Default: ``600``


``osd op log threshold``

:Description: How many operations logs to display at once.
:Type: 32-bit Integer
:Default: ``5``

.. index:: OSD; backfilling

Backfilling
===========

When you add or remove Ceph OSD Daemons to a cluster, the CRUSH algorithm will
want to rebalance the cluster by moving placement groups to or from Ceph OSD
Daemons to restore the balance. The process of migrating placement groups and
the objects they contain can reduce the cluster's operational performance
considerably. To maintain operational performance, Ceph performs this migration
with 'backfilling', which allows Ceph to set backfill operations to a lower
priority than requests to read or write data. 


``osd max backfills``

:Description: The maximum number of backfills allowed to or from a single OSD.
:Type: 64-bit Unsigned Integer
:Default: ``10``


``osd backfill scan min`` 

:Description: The scan interval in seconds for backfill operations when cluster 
              load is low.
:Type: 32-bit Integer
:Default: ``64`` 


``osd backfill scan max`` 

:Description: The maximum scan interval in seconds for backfill operations 
              irrespective of cluster load.

:Type: 32-bit Integer
:Default: ``512`` 


``osd backfill full ratio``

:Description: Refuse to accept backfill requests when the Ceph OSD Daemon's 
              full ratio is above this value.

:Type: Float
:Default: ``0.85``


``osd backfill retry interval``

:Description: The number of seconds to wait before retrying backfill requests.
:Type: Double
:Default: ``10.0``

.. index:: OSD; osdmap

OSD Map
=======

OSD maps reflect the OSD daemons operating in the cluster. Over time, the 
number of map epochs increases. Ceph provides some settings to ensure that
Ceph performs well as the OSD map grows larger.


``osd map dedup``

:Description: Enable removing duplicates in the OSD map. 
:Type: Boolean
:Default: ``true``


``osd map cache size`` 

:Description: The size of the OSD map cache in megabytes.
:Type: 32-bit Integer
:Default: ``500``


``osd map cache bl size``

:Description: The size of the in-memory OSD map cache in OSD daemons. 
:Type: 32-bit Integer
:Default: ``50``


``osd map cache bl inc size``

:Description: The size of the in-memory OSD map cache incrementals in 
              OSD daemons.

:Type: 32-bit Integer
:Default: ``100``


``osd map message max`` 

:Description: The maximum map entries allowed per MOSDMap message.
:Type: 32-bit Integer
:Default: ``100``

.. index:: OSD; recovery

Recovery
========

When the cluster starts or when a Ceph OSD Daemon crashes and restarts, the OSD
begins peering with other Ceph OSD Daemons before writes can occur.  See
`Monitoring OSDs and PGs`_ for details.

If a Ceph OSD Daemon crashes and comes back online, usually it will be out of
sync with other Ceph OSD Daemons containing more recent versions of objects in
the placement groups. When this happens, the Ceph OSD Daemon goes into recovery
mode and seeks to get the latest copy of the data and bring its map back up to
date. Depending upon how long the Ceph OSD Daemon was down, the OSD's objects
and placement groups may be significantly out of date. Also, if a failure domain
went down (e.g., a rack), more than one Ceph OSD Daemon may come back online at
the same time. This can make the recovery process time consuming and resource
intensive.

To maintain operational performance, Ceph performs recovery with limitations on
the number recovery requests, threads and object chunk sizes which allows Ceph
perform well in a degraded state. 


``osd recovery delay start`` 

:Description: After peering completes, Ceph will delay for the specified number 
              of seconds before starting to recover objects.

:Type: Float
:Default: ``15`` 


``osd recovery max active`` 

:Description: The number of active recovery requests per OSD at one time. More 
              requests will accelerate recovery, but the requests places an 
              increased load on the cluster.

:Type: 32-bit Integer
:Default: ``5``


``osd recovery max chunk`` 

:Description: The maximum size of a recovered chunk of data to push. 
:Type: 64-bit Integer Unsigned
:Default: ``1 << 20`` 


``osd recovery threads`` 

:Description: The number of threads for recovering data.
:Type: 32-bit Integer
:Default: ``1``


``osd recovery thread timeout`` 

:Description: The maximum time in seconds before timing out a recovery thread.
:Type: 32-bit Integer
:Default: ``30``


``osd recover clone overlap``

:Description: Preserves clone overlap during recovery. Should always be set 
              to ``true``.

:Type: Boolean
:Default: ``true``



Miscellaneous
=============


``osd snap trim thread timeout`` 

:Description: The maximum time in seconds before timing out a snap trim thread.
:Type: 32-bit Integer
:Default: ``60*60*1`` 


``osd backlog thread timeout`` 

:Description: The maximum time in seconds before timing out a backlog thread.
:Type: 32-bit Integer
:Default: ``60*60*1`` 


``osd default notify timeout`` 

:Description: The OSD default notification timeout (in seconds).
:Type: 32-bit Integer Unsigned
:Default: ``30`` 


``osd check for log corruption`` 

:Description: Check log files for corruption. Can be computationally expensive.
:Type: Boolean
:Default: ``false`` 


``osd remove thread timeout`` 

:Description: The maximum time in seconds before timing out a remove OSD thread.
:Type: 32-bit Integer
:Default: ``60*60``


``osd command thread timeout`` 

:Description: The maximum time in seconds before timing out a command thread.
:Type: 32-bit Integer
:Default: ``10*60`` 


``osd command max records`` 

:Description: Limits the number of lost objects to return. 
:Type: 32-bit Integer
:Default: ``256`` 


``osd auto upgrade tmap`` 

:Description: Uses ``tmap`` for ``omap`` on old objects.
:Type: Boolean
:Default: ``true``
 

``osd tmapput sets users tmap`` 

:Description: Uses ``tmap`` for debugging only.
:Type: Boolean
:Default: ``false`` 


``osd preserve trimmed log``

:Description: Preserves trimmed log files, but uses more disk space.
:Type: Boolean
:Default: ``false``



.. _pool: ../../operations/pools
.. _Configuring Monitor/OSD Interaction: ../mon-osd-interaction
.. _Monitoring OSDs and PGs: ../../operations/monitoring-osd-pg#peering
.. _Pool & PG Config Reference: ../pool-pg-config-ref
.. _Journal Config Reference: ../journal-ref