Hi,
AFAIU, you can’t migrate back to the slow device. It’s either
migrating from the slow device to a fast device or remove between fast
devices. I’m not aware that your scenario was considered in that tool.
The docs don’t specifically say that, but they also don’t mention
going back to slow device only. Someone please correct me, but I’d say
you’ll have to rebuild that OSD to detach it from the fast device.
Regards,
Eugen
Zitat von Chris Dunlop <chris@xxxxxxxxxxxx>:
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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