Using different device classes

To create performance domains, use device classes and a single CRUSH hierarchy.

To create performance domains, add OSDs to the CRUSH hierarchy, then do the following:

1. Add a class to each device. For example:

   Syntax

    ceph osd crush set-device-class <class> <osdId> [<osdId>]
    ceph osd crush set-device-class hdd osd.0 osd.1 osd.4 osd.5
    ceph osd crush set-device-class ssd osd.2 osd.3 osd.6 osd.7

2. Then, create rules to use the devices.

   Syntax

    ceph osd crush rule create-replicated <rule-name> <root> <failure-domain-type> <class>
    ceph osd crush rule create-replicated cold default host hdd
    ceph osd crush rule create-replicated hot default host ssd

3. Finally, set pools to use the rules.

   Syntax

    ceph osd pool set <poolname> crush_rule <rule-name>
    ceph osd pool set cold_tier crush_rule cold
    ceph osd pool set hot_tier crush_rule hot