Input and output options

Understand the input and output (I/O) options for Ceph Block Devices.

Table 1 lists the block-list configuration options for Ceph Block Devices.

Table 1. I/O configuration options
Option	Description	Type	Required	Values	Default
`rbd_compression_hint`	Hint to send to the OSDs on write operations. If set to `compressible` and the OSD `bluestore_compression_mode` setting is `passive`, the OSD attempts to compress data. If set to `incompressible` and the OSD `bluestore_compression_mode` setting is `aggressive`, the OSD does not attempt to compress data.	Enum	No	`none` `compressible` `incompressible`	`none`
`rbd_read_from_replica_policy`	Policy for determining which OSD receives read operations. If set to `default`, each PG’s primary OSD will always be used for read operations. If set to `balance`, read operations are sent to a randomly selected OSD within the replica set. If set to `localize`, read operations are sent to the closest OSD as determined by the CRUSH map and the `crush_location` configuration option, where the `crush_location` is denoted by using `key=value`. The `key` aligns with the CRUSH map keys. Note: This feature requires the storage cluster to be configured with a minimum compatible OSD release of the latest version of IBM Storage Ceph.	Enum	No	`default` `balance` `localize`	`default`