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.


	# 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 = 4  # Write an object 4 times.
	osd pool default min size = 1 # Allow writing one copy 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.

mon pg create interval

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

mon pg stuck threshold

Description:Number of seconds after which PGs can be considered as being stuck.
Type:32-bit Integer

osd pg bits

Description:Placement group bits per Ceph OSD Daemon.
Type:32-bit Integer

osd pgp bits

Description:The number of bits per Ceph OSD Daemon for PGPs.
Type:32-bit Integer

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.
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 replicated ruleset

Description:The default CRUSH ruleset to use when creating a replicated pool.
Type:8-bit Integer
Default:CEPH_DEFAULT_CRUSH_REPLICATED_RULESET, which means “pick a ruleset with the lowest numerical ID and use that”. This is to make pool creation work in the absence of ruleset 0.

osd pool erasure code stripe width

Description:Sets the desired size, in bytes, of an object stripe on every erasure coded pools. Every object if size S will be stored as N stripes and each stripe will be encoded/decoded individually.
Type:Unsigned 32-bit Integer

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

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. 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

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

osd pool default flags

Description:The default flags for new pools.
Type:32-bit Integer

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
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

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