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[ceph.git] / 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 ``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., ``host``), enter  it in an OSD-specific section of your configuration
file. For example:

.. code-block:: ini

	[osd]
		osd journal size = 5120

	[osd.0]
		host = osd-host-a

	[osd.1]
		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.

.. warning:: **DO NOT** change 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 max object size``

:Description: The maximum size of a RADOS object in bytes.
:Type: 32-bit Unsigned Integer
:Default: 128MB


``osd client message size cap``

:Description: The largest client data message allowed in memory.
:Type: 64-bit Unsigned Integer
: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; file system

File System Settings
====================
Ceph builds and mounts file systems which are used for Ceph OSDs.

``osd mkfs options {fs-type}``

:Description: Options used when creating a new Ceph OSD of type {fs-type}.

:Type: String
:Default for xfs: ``-f -i 2048``
:Default for other file systems: {empty string}

For example::
  ``osd mkfs options xfs = -f -d agcount=24``

``osd mount options {fs-type}``

:Description: Options used when mounting a Ceph OSD of type {fs-type}.

:Type: String
:Default for xfs: ``rw,noatime,inode64``
:Default for other file systems: ``rw, noatime``

For example::
  ``osd mount options xfs = rw, noatime, inode64, logbufs=8``


.. 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

When using a single device type (for example, spinning drives), the journals
should be *colocated*: the logical volume (or partition) should be in the same
device as the ``data`` logical volume.

When using a mix of fast (SSDs, NVMe) devices with slower ones (like spinning
drives) it makes sense to place the journal on the faster device, while
``data`` occupies the slower device fully.

The default ``osd journal size`` value is 5120 (5 gigabytes), but it can be
larger, in which case it will need to be set in the ``ceph.conf`` file::


	osd journal size = 10240


``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.

:Type: 32-bit Integer
:Default: ``5120``


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 begin hour``

:Description: The time of day for the lower bound when a scheduled scrub can be
              performed.
:Type: Integer in the range of 0 to 24
:Default: ``0``


``osd scrub end hour``

:Description: The time of day for the upper bound when a scheduled scrub can be
              performed. Along with ``osd scrub begin hour``, they define a time
              window, in which the scrubs can happen. But a scrub will be performed
              no matter the time window allows or not, as long as the placement
              group's scrub interval exceeds ``osd scrub max interval``.
:Type: Integer in the range of 0 to 24
:Default: ``24``


``osd scrub begin week day``

:Description: This restricts scrubbing to this day of the week or later.
              0 or 7 = Sunday, 1 = Monday, etc.
:Type: Integer in the range of 0 to 7
:Default: ``0``


``osd scrub end week day``

:Description: This restricts scrubbing to days of the week earlier than this.
              0 or 7 = Sunday, 1 = Monday, etc.
:Type: Integer in the range of 0 to 7
:Default: ``7``


``osd scrub during recovery``

:Description: Allow scrub during recovery. Setting this to ``false`` will disable
              scheduling new scrub (and deep--scrub) while there is active recovery.
              Already running scrubs will be continued. This might be useful to reduce
              load on busy clusters.
:Type: Boolean
:Default: ``true``


``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 normalized maximum load. Ceph will not scrub when the system load
              (as defined by ``getloadavg() / number of online cpus``) is higher than this number.
              Default is ``0.5``.

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


``osd scrub min interval``

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

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


``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 week. ``7*60*60*24``


``osd scrub chunk min``

:Description: The minimal number of object store chunks to scrub during single operation.
              Ceph blocks writes to single chunk during scrub.

:Type: 32-bit Integer
:Default: 5


``osd scrub chunk max``

:Description: The maximum number of object store chunks to scrub during single operation.

:Type: 32-bit Integer
:Default: 25


``osd scrub sleep``

:Description: Time to sleep before scrubbing next group of chunks. Increasing this value will slow
              down whole scrub operation while client operations will be less impacted.

:Type: Float
:Default: 0


``osd deep scrub interval``

:Description: The interval for "deep" scrubbing (fully reading all data). The
              ``osd scrub load threshold`` does not affect this setting.

:Type: Float
:Default: Once per week.  ``60*60*24*7``


``osd scrub interval randomize ratio``

:Description: Add a random delay to ``osd scrub min interval`` when scheduling
              the next scrub job for a placement group. The delay is a random
              value less than ``osd scrub min interval`` \*
              ``osd scrub interval randomized ratio``. So the default setting
              practically randomly spreads the scrubs out in the allowed time
              window of ``[1, 1.5]`` \* ``osd scrub min interval``.
:Type: Float
:Default: ``0.5``

``osd deep scrub stride``

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


``osd scrub auto repair``

:Description: Setting this to ``true`` will enable automatic pg repair when errors
              are found in scrub or deep-scrub.  However, if more than
              ``osd scrub auto repair num errors`` errors are found a repair is NOT performed.
:Type: Boolean
:Default: ``false``


``osd scrub auto repair num errors``

:Description: Auto repair will not occur if more than this many errors are found.
:Type: 32-bit Integer
:Default: ``5``


.. index:: OSD; operations settings

Operations
==========

``osd op queue``

:Description: This sets the type of queue to be used for prioritizing ops
              in the OSDs. Both queues feature a strict sub-queue which is
              dequeued before the normal queue. The normal queue is different
              between implementations. The original PrioritizedQueue (``prio``) uses a
              token bucket system which when there are sufficient tokens will
              dequeue high priority queues first. If there are not enough
              tokens available, queues are dequeued low priority to high priority.
              The WeightedPriorityQueue (``wpq``) dequeues all priorities in
              relation to their priorities to prevent starvation of any queue.
              WPQ should help in cases where a few OSDs are more overloaded
              than others. The new mClock based OpClassQueue
              (``mclock_opclass``) prioritizes operations based on which class
              they belong to (recovery, scrub, snaptrim, client op, osd subop).
              And, the mClock based ClientQueue (``mclock_client``) also
              incorporates the client identifier in order to promote fairness
              between clients. See `QoS Based on mClock`_. Requires a restart.

:Type: String
:Valid Choices: prio, wpq, mclock_opclass, mclock_client
:Default: ``prio``


``osd op queue cut off``

:Description: This selects which priority ops will be sent to the strict
              queue verses the normal queue. The ``low`` setting sends all
              replication ops and higher to the strict queue, while the ``high``
              option sends only replication acknowledgement ops and higher to
              the strict queue. Setting this to ``high`` should help when a few
              OSDs in the cluster are very busy especially when combined with
              ``wpq`` in the ``osd op queue`` setting. OSDs that are very busy
              handling replication traffic could starve primary client traffic
              on these OSDs without these settings. Requires a restart.

:Type: String
:Valid Choices: low, high
:Default: ``low``


``osd client op priority``

:Description: The priority set for client operations.

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


``osd recovery op priority``

:Description: The priority set for recovery operations, if not specified by the pool's ``recovery_op_priority``.

:Type: 32-bit Integer
:Default: ``3``
:Valid Range: 1-63


``osd scrub priority``

:Description: The default priority set for a scheduled scrub work queue when the
              pool doesn't specify a value of ``scrub_priority``.  This can be
              boosted to the value of ``osd client op priority`` when scrub is
              blocking client operations.

:Type: 32-bit Integer
:Default: ``5``
:Valid Range: 1-63


``osd requested scrub priority``

:Description: The priority set for user requested scrub on the work queue.  If
              this value were to be smaller than ``osd client op priority`` it
              can be boosted to the value of ``osd client op priority`` when
              scrub is blocking client operations.

:Type: 32-bit Integer
:Default: ``120``


``osd snap trim priority``

:Description: The priority set for the snap trim work queue.

:Type: 32-bit Integer
:Default: ``5``
:Valid Range: 1-63

``osd snap trim sleep``

:Description: Time in seconds to sleep before next snap trim op.
              Increasing this value will slow down snap trimming.
              This option overrides backend specific variants.

:Type: Float
:Default: ``0``


``osd snap trim sleep hdd``

:Description: Time in seconds to sleep before next snap trim op
              for HDDs.

:Type: Float
:Default: ``5``


``osd snap trim sleep ssd``

:Description: Time in seconds to sleep before next snap trim op
              for SSDs.

:Type: Float
:Default: ``0``


``osd snap trim sleep hybrid``

:Description: Time in seconds to sleep before next snap trim op
              when osd data is on HDD and osd journal is on SSD.

:Type: Float
:Default: ``2``

``osd op thread timeout``

:Description: The Ceph OSD Daemon operation thread timeout in seconds.
:Type: 32-bit Integer
:Default: ``15``


``osd op complaint time``

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

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


``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``


QoS Based on mClock
-------------------

Ceph's use of mClock is currently in the experimental phase and should
be approached with an exploratory mindset.

Core Concepts
`````````````

The QoS support of Ceph is implemented using a queueing scheduler
based on `the dmClock algorithm`_. This algorithm allocates the I/O
resources of the Ceph cluster in proportion to weights, and enforces
the constraints of minimum reservation and maximum limitation, so that
the services can compete for the resources fairly. Currently the
*mclock_opclass* operation queue divides Ceph services involving I/O
resources into following buckets:

- client op: the iops issued by client
- osd subop: the iops issued by primary OSD
- snap trim: the snap trimming related requests
- pg recovery: the recovery related requests
- pg scrub: the scrub related requests

And the resources are partitioned using following three sets of tags. In other
words, the share of each type of service is controlled by three tags:

#. reservation: the minimum IOPS allocated for the service.
#. limitation: the maximum IOPS allocated for the service.
#. weight: the proportional share of capacity if extra capacity or system
   oversubscribed.

In Ceph operations are graded with "cost". And the resources allocated
for serving various services are consumed by these "costs". So, for
example, the more reservation a services has, the more resource it is
guaranteed to possess, as long as it requires. Assuming there are 2
services: recovery and client ops:

- recovery: (r:1, l:5, w:1)
- client ops: (r:2, l:0, w:9)

The settings above ensure that the recovery won't get more than 5
requests per second serviced, even if it requires so (see CURRENT
IMPLEMENTATION NOTE below), and no other services are competing with
it. But if the clients start to issue large amount of I/O requests,
neither will they exhaust all the I/O resources. 1 request per second
is always allocated for recovery jobs as long as there are any such
requests. So the recovery jobs won't be starved even in a cluster with
high load. And in the meantime, the client ops can enjoy a larger
portion of the I/O resource, because its weight is "9", while its
competitor "1". In the case of client ops, it is not clamped by the
limit setting, so it can make use of all the resources if there is no
recovery ongoing.

Along with *mclock_opclass* another mclock operation queue named
*mclock_client* is available. It divides operations based on category
but also divides them based on the client making the request. This
helps not only manage the distribution of resources spent on different
classes of operations but also tries to insure fairness among clients.

CURRENT IMPLEMENTATION NOTE: the current experimental implementation
does not enforce the limit values. As a first approximation we decided
not to prevent operations that would otherwise enter the operation
sequencer from doing so.

Subtleties of mClock
````````````````````

The reservation and limit values have a unit of requests per
second. The weight, however, does not technically have a unit and the
weights are relative to one another. So if one class of requests has a
weight of 1 and another a weight of 9, then the latter class of
requests should get 9 executed at a 9 to 1 ratio as the first class.
However that will only happen once the reservations are met and those
values include the operations executed under the reservation phase.

Even though the weights do not have units, one must be careful in
choosing their values due how the algorithm assigns weight tags to
requests. If the weight is *W*, then for a given class of requests,
the next one that comes in will have a weight tag of *1/W* plus the
previous weight tag or the current time, whichever is larger. That
means if *W* is sufficiently large and therefore *1/W* is sufficiently
small, the calculated tag may never be assigned as it will get a value
of the current time. The ultimate lesson is that values for weight
should not be too large. They should be under the number of requests
one expects to ve serviced each second.

Caveats
```````

There are some factors that can reduce the impact of the mClock op
queues within Ceph. First, requests to an OSD are sharded by their
placement group identifier. Each shard has its own mClock queue and
these queues neither interact nor share information among them. The
number of shards can be controlled with the configuration options
``osd_op_num_shards``, ``osd_op_num_shards_hdd``, and
``osd_op_num_shards_ssd``. A lower number of shards will increase the
impact of the mClock queues, but may have other deleterious effects.

Second, requests are transferred from the operation queue to the
operation sequencer, in which they go through the phases of
execution. The operation queue is where mClock resides and mClock
determines the next op to transfer to the operation sequencer. The
number of operations allowed in the operation sequencer is a complex
issue. In general we want to keep enough operations in the sequencer
so it's always getting work done on some operations while it's waiting
for disk and network access to complete on other operations. On the
other hand, once an operation is transferred to the operation
sequencer, mClock no longer has control over it. Therefore to maximize
the impact of mClock, we want to keep as few operations in the
operation sequencer as possible. So we have an inherent tension.

The configuration options that influence the number of operations in
the operation sequencer are ``bluestore_throttle_bytes``,
``bluestore_throttle_deferred_bytes``,
``bluestore_throttle_cost_per_io``,
``bluestore_throttle_cost_per_io_hdd``, and
``bluestore_throttle_cost_per_io_ssd``.

A third factor that affects the impact of the mClock algorithm is that
we're using a distributed system, where requests are made to multiple
OSDs and each OSD has (can have) multiple shards. Yet we're currently
using the mClock algorithm, which is not distributed (note: dmClock is
the distributed version of mClock).

Various organizations and individuals are currently experimenting with
mClock as it exists in this code base along with their modifications
to the code base. We hope you'll share you're experiences with your
mClock and dmClock experiments in the ceph-devel mailing list.


``osd push per object cost``

:Description: the overhead for serving a push op

:Type: Unsigned Integer
:Default: 1000

``osd recovery max chunk``

:Description: the maximum total size of data chunks a recovery op can carry.

:Type: Unsigned Integer
:Default: 8 MiB


``osd op queue mclock client op res``

:Description: the reservation of client op.

:Type: Float
:Default: 1000.0


``osd op queue mclock client op wgt``

:Description: the weight of client op.

:Type: Float
:Default: 500.0


``osd op queue mclock client op lim``

:Description: the limit of client op.

:Type: Float
:Default: 1000.0


``osd op queue mclock osd subop res``

:Description: the reservation of osd subop.

:Type: Float
:Default: 1000.0


``osd op queue mclock osd subop wgt``

:Description: the weight of osd subop.

:Type: Float
:Default: 500.0


``osd op queue mclock osd subop lim``

:Description: the limit of osd subop.

:Type: Float
:Default: 0.0


``osd op queue mclock snap res``

:Description: the reservation of snap trimming.

:Type: Float
:Default: 0.0


``osd op queue mclock snap wgt``

:Description: the weight of snap trimming.

:Type: Float
:Default: 1.0


``osd op queue mclock snap lim``

:Description: the limit of snap trimming.

:Type: Float
:Default: 0.001


``osd op queue mclock recov res``

:Description: the reservation of recovery.

:Type: Float
:Default: 0.0


``osd op queue mclock recov wgt``

:Description: the weight of recovery.

:Type: Float
:Default: 1.0


``osd op queue mclock recov lim``

:Description: the limit of recovery.

:Type: Float
:Default: 0.001


``osd op queue mclock scrub res``

:Description: the reservation of scrub jobs.

:Type: Float
:Default: 0.0


``osd op queue mclock scrub wgt``

:Description: the weight of scrub jobs.

:Type: Float
:Default: 1.0


``osd op queue mclock scrub lim``

:Description: the limit of scrub jobs.

:Type: Float
:Default: 0.001

.. _the dmClock algorithm: https://www.usenix.org/legacy/event/osdi10/tech/full_papers/Gulati.pdf


.. 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: ``1``


``osd backfill scan min``

:Description: The minimum number of objects per backfill scan.

:Type: 32-bit Integer
:Default: ``64``


``osd backfill scan max``

:Description: The maximum number of objects per backfill scan.

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


``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 number of OSD maps to keep cached.
:Type: 32-bit Integer
:Default: ``50``


``osd map message max``

:Description: The maximum map entries allowed per MOSDMap message.
:Type: 32-bit Integer
:Default: ``40``



.. 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: ``0``


``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: ``3``


``osd recovery max chunk``

:Description: The maximum size of a recovered chunk of data to push.
:Type: 64-bit Unsigned Integer
:Default: ``8 << 20``


``osd recovery max single start``

:Description: The maximum number of recovery operations per OSD that will be
              newly started when an OSD is recovering.
:Type: 64-bit Unsigned 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``


``osd recovery sleep``

:Description: Time in seconds to sleep before next recovery or backfill op.
              Increasing this value will slow down recovery operation while
              client operations will be less impacted.

:Type: Float
:Default: ``0``


``osd recovery sleep hdd``

:Description: Time in seconds to sleep before next recovery or backfill op
              for HDDs.

:Type: Float
:Default: ``0.1``


``osd recovery sleep ssd``

:Description: Time in seconds to sleep before next recovery or backfill op
              for SSDs.

:Type: Float
:Default: ``0``


``osd recovery sleep hybrid``

:Description: Time in seconds to sleep before next recovery or backfill op
              when osd data is on HDD and osd journal is on SSD.

:Type: Float
:Default: ``0.025``


``osd recovery priority``

:Description: The default priority set for recovery work queue.  Not
              related to a pool's ``recovery_priority``.

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


Tiering
=======

``osd agent max ops``

:Description: The maximum number of simultaneous flushing ops per tiering agent
              in the high speed mode.
:Type: 32-bit Integer
:Default: ``4``


``osd agent max low ops``

:Description: The maximum number of simultaneous flushing ops per tiering agent
              in the low speed mode.
:Type: 32-bit Integer
:Default: ``2``

See `cache target dirty high ratio`_ for when the tiering agent flushes dirty
objects within the high speed mode.

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 Unsigned Integer
: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 fast fail on connection refused``

:Description: If this option is enabled, crashed OSDs are marked down
              immediately by connected peers and MONs (assuming that the
              crashed OSD host survives). Disable it to restore old
              behavior, at the expense of possible long I/O stalls when
              OSDs crash in the middle of I/O operations.
:Type: Boolean
:Default: ``true``



.. _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
.. _cache target dirty high ratio: ../../operations/pools#cache-target-dirty-high-ratio