Ok, further testing and thinking...
Frank, you mentioned about creating the osd without cache so that it'd
be picked up as HDD not SSD. Also back in this thread Aleksandr
mentioned that the parameter rotational in sysfs is used for this.
So I checked what this parameter is being set to with bcache with and
without a cache disk attached. It's always set to zero. However I also
noticed that since this is in the "virtual" disks section this
parameter is writable.
e.g.
$ echo 1 | sudo tee /sys/devices/virtual/block/bcache0/queue/rotational
1
$ cat /sys/devices/virtual/block/bcache0/queue/rotational
1
So then I did some testing on my test cluster and created an osd on
this bcache disk set to rotational=1. The class gets correctly set to
HDD and when I query the osd metadata I get rotational=1
$ sudo ceph osd metadata 15
--->8---
"bluefs_db_rotational": "0",
"bluefs_db_type": "ssd",
--->8---
"bluestore_bdev_rotational": "1",
"bluestore_bdev_type": "hdd",
--->8---
"devices": "bcache0,md1",
--->8---
"osd_data": "/var/lib/ceph/osd/ceph-15",
"osd_objectstore": "bluestore",
"rotational": "1"
So that's looking pretty good for working around the issue for me.
I'll need to do a bunch more testing as it'll obviously be changing a
few other settings that weren't getting set before on osd creation.
It's an easy add to my process though. After creating bcache device,
set rotational to 1 and carry on as before.
Rich
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