Re: Crush Rules with multiple Device Classes

[Konstantin Shalygin <k0ste@xxxxxxxx>]

Now my first question is: 
1) Is there a way to specify "take default class (ssd or nvme)"? 
   Then we could just do this for the migration period, and at some point remove "ssd". 

If multi-device-class in a crush rule is not supported yet, the only workaround which comes to my mind right now is to issue:
  $ ceph osd crush set-device-class nvme <old_ssd_osd>
for all our old SSD-backed osds, and modify the crush rule to refer to class "nvme" straightaway. 

My advice is to set class to 'nvme' to your current osd's with class 'ssd' and change crush rule to this class.

You still have to do it, better sooner than later. Either use the ssd class for your future drives, in case when you switch all your ssd to nvme and forgot about ssd disks.

Here my third question:
3) Are the tunables used for NVME devices the same as for SSD devices?
   I do not find any NVME tunables here:
   http://docs.ceph.com/docs/master/rados/configuration/osd-config-ref/
   Only SSD, HDD and Hybrid are shown. 

Ceph is doesn't care about nvme/ssd. Ceph is only care is_rotational drive or not.

    "bluefs_db_rotational": "0",
    "bluefs_slow_rotational": "1",
    "bluefs_wal_rotational": "0",
    "bluestore_bdev_rotational": "1",
    "journal_rotational": "0",
    "rotational": "1"

k

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