Hi,
What's the correct way to migrate an OSD wal/db from a fast device to the
(slow) block device?
I have an osd with wal/db on a fast LV device and block on a slow LV
device. I want to move the wal/db onto the block device so I can
reconfigure the fast device before moving the wal/db back to the fast
device.
This link says to use "ceph-volume lvm migrate" (I'm on pacific, but the
quincy and reef docs are the same):
https://docs.ceph.com/en/pacific/ceph-volume/lvm/migrate/
I tried:
$ cephadm unit --fsid ${fsid} --name osd.${osdid} stop
$ cephadm shell --fsid ${fsid} --name osd.${osdid} -- \
ceph-volume lvm migrate --osd-id ${osdid} --osd-fsid ${osd_fsid} \
--from db wal --target ${block_vglv}
$ systemctl stop ${osd_service}
$ systemctl start ${osd_service}
"cephadm ceph-volume lvm list" now shows only the (slow) block device
whereas before the migrate it was showing both the block and db devices.
However "lsof" shows the new osd process still has the original fast
wal/db device open and "iostat" shows this device is still getting i/o.
Also:
$ ls -l /var/lib/ceph/${fsid}/osd.${osdid}/block*
...shows both the "block" and "block.db" symlinks to the original separate devices.
And there are now no lv_tags on the original wal/db LV:
$ lvs -o lv_tags ${original_db_vg_lv}
Now I'm concerned there's device mismatch for this osd: "cephadm
ceph-volume lvm list" believes there's no separate wal/db, but the osd is
currently *using* the original separate wal/db.
I guess if the server were to restart this osd would be in all sorts of
trouble.
What's going on there, and what can be done to fix it? Is it a matter of
recreating the tags on the original db device? (But then what happens to
whatever did get migrated to the block device - e.g. is that space lost?)
Or is it a matter of using ceph-bluestore-tool to do a
bluefs-bdev-migrate, e.g. something like:
$ cephadm unit --fsid ${fsid} --name osd.${osdid} stop
$ osddir=/var/lib/ceph/osd/ceph-${osdid}
$ cephadm shell --fsid ${fsid} --name osd.${osdid} -- \
ceph-bluestore-tool --path ${osddir} --devs-source ${osddir}/block.db \
--dev-target ${osddir}/block bluefs-bdev-migrate
$ rm /var/lib/ceph/${fsid}/osd.${osdid}/block.db
$ systemctl stop ${osd_service}
$ systemctl start ${osd_service}
Or... something else?
And how *should* moving the wal/db be done?
Cheers,
Chris
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