Pool, PG and CRUSH Config Reference

When you create pools and set the number of placement groups for the pool, Ceph uses default values when you don’t specifically override the defaults. We recommend overridding some of the defaults. Specifically, we recommend setting a pool’s replica size and overriding the default number of placement groups. You can specifically set these values when running pool commands. You can also override the defaults by adding new ones in the [global] section of your Ceph configuration file.

[global]

	# By default, Ceph makes 3 replicas of objects. If you want to make four
	# copies of an object the default value--a primary copy and three replica
	# copies--reset the default values as shown in 'osd pool default size'.
	# If you want to allow Ceph to write a lesser number of copies in a degraded
	# state, set 'osd pool default min size' to a number less than the
	# 'osd pool default size' value.

	osd pool default size = 3  # Write an object 3 times.
	osd pool default min size = 2 # Allow writing two copies in a degraded state.

	# Ensure you have a realistic number of placement groups. We recommend
	# approximately 100 per OSD. E.g., total number of OSDs multiplied by 100
	# divided by the number of replicas (i.e., osd pool default size). So for
	# 10 OSDs and osd pool default size = 4, we'd recommend approximately
	# (100 * 10) / 4 = 250.

	osd pool default pg num = 250
	osd pool default pgp num = 250

mon max pool pg num

Description

The maximum number of placement groups per pool.

Type

Integer

Default

65536

mon pg create interval

Description

Number of seconds between PG creation in the same Ceph OSD Daemon.

Type

Float

Default

30.0

mon pg stuck threshold

Description

Number of seconds after which PGs can be considered as being stuck.

Type

32-bit Integer

Default

300

mon pg min inactive

Description

Issue a HEALTH_ERR in cluster log if the number of PGs stay inactive longer than mon_pg_stuck_threshold exceeds this setting. A non-positive number means disabled, never go into ERR.

Type

Integer

Default

1

mon pg warn min per osd

Description

Issue a HEALTH_WARN in cluster log if the average number of PGs per (in) OSD is under this number. (a non-positive number disables this)

Type

Integer

Default

30

mon pg warn max per osd

Description

Issue a HEALTH_WARN in cluster log if the average number of PGs per (in) OSD is above this number. (a non-positive number disables this)

Type

Integer

Default

300

mon pg warn min objects

Description

Do not warn if the total number of objects in cluster is below this number

Type

Integer

Default

1000

mon pg warn min pool objects

Description

Do not warn on pools whose object number is below this number

Type

Integer

Default

1000

mon pg check down all threshold

Description

Threshold of down OSDs percentage after which we check all PGs for stale ones.

Type

Float

Default

0.5

mon pg warn max object skew

Description

Issue a HEALTH_WARN in cluster log if the average object number of a certain pool is greater than mon pg warn max object skew times the average object number of the whole pool. (a non-positive number disables this)

Type

Float

Default

10

mon delta reset interval

Description

Seconds of inactivity before we reset the pg delta to 0. We keep track of the delta of the used space of each pool, so, for example, it would be easier for us to understand the progress of recovery or the performance of cache tier. But if there’s no activity reported for a certain pool, we just reset the history of deltas of that pool.

Type

Integer

Default

10

mon osd max op age

Description

Maximum op age before we get concerned (make it a power of 2). A HEALTH_WARN will be issued if a request has been blocked longer than this limit.

Type

Float

Default

32.0

osd pg bits

Description

Placement group bits per Ceph OSD Daemon.

Type

32-bit Integer

Default

6

osd pgp bits

Description

The number of bits per Ceph OSD Daemon for PGPs.

Type

32-bit Integer

Default

6

osd crush chooseleaf type

Description

The bucket type to use for chooseleaf in a CRUSH rule. Uses ordinal rank rather than name.

Type

32-bit Integer

Default

1. Typically a host containing one or more Ceph OSD Daemons.

osd crush initial weight

Description

The initial crush weight for newly added osds into crushmap.

Type

Double

Default

the size of newly added osd in TB. By default, the initial crush weight for the newly added osd is set to its volume size in TB. See Weighting Bucket Items for details.

osd pool default crush rule

Description

The default CRUSH rule to use when creating a replicated pool.

Type

8-bit Integer

Default

-1, which means “pick the rule with the lowest numerical ID and use that”. This is to make pool creation work in the absence of rule 0.

osd pool erasure code stripe unit

Description

Sets the default size, in bytes, of a chunk of an object stripe for erasure coded pools. Every object of size S will be stored as N stripes, with each data chunk receiving stripe unit bytes. Each stripe of N * stripe unit bytes will be encoded/decoded individually. This option can is overridden by the stripe_unit setting in an erasure code profile.

Type

Unsigned 32-bit Integer

Default

4096

osd pool default size

Description

Sets the number of replicas for objects in the pool. The default value is the same as ceph osd pool set {pool-name} size {size}.

Type

32-bit Integer

Default

3

osd pool default min size

Description

Sets the minimum number of written replicas for objects in the pool in order to acknowledge a write operation to the client. If minimum is not met, Ceph will not acknowledge the write to the client, which may result in data loss. This setting ensures a minimum number of replicas when operating in degraded mode.

Type

32-bit Integer

Default

0, which means no particular minimum. If 0, minimum is size - (size / 2).

osd pool default pg num

Description

The default number of placement groups for a pool. The default value is the same as pg_num with mkpool.

Type

32-bit Integer

Default

8

osd pool default pgp num

Description

The default number of placement groups for placement for a pool. The default value is the same as pgp_num with mkpool. PG and PGP should be equal (for now).

Type

32-bit Integer

Default

8

osd pool default flags

Description

The default flags for new pools.

Type

32-bit Integer

Default

0

osd max pgls

Description

The maximum number of placement groups to list. A client requesting a large number can tie up the Ceph OSD Daemon.

Type

Unsigned 64-bit Integer

Default

1024

Note

Default should be fine.

osd min pg log entries

Description

The minimum number of placement group logs to maintain when trimming log files.

Type

32-bit Int Unsigned

Default

1000

osd default data pool replay window

Description

The time (in seconds) for an OSD to wait for a client to replay a request.

Type

32-bit Integer

Default

45

osd max pg per osd hard ratio

Description

The ratio of number of PGs per OSD allowed by the cluster before OSD refuses to create new PGs. OSD stops creating new PGs if the number of PGs it serves exceeds osd max pg per osd hard ratio * mon max pg per osd.

Type

Float

Default

2

osd recovery priority

Description

Priority of recovery in the work queue.

Type

Integer

Default

5

osd recovery op priority

Description

Default priority used for recovery operations if pool doesn’t override.

Type

Integer

Default

3