Hi Igor,
On 15/11/2019 14:22, Igor Fedotov wrote:
Do you mean both standalone DB and(!!) standalone WAL devices/partitions
by having SSD DB/WAL?
No, 1x combined DB/WAL partition on an SSD and 1x data partition on an
HDD per OSD. I.e. created like:
ceph-deploy osd create --data /dev/sda --block-db ssd0/ceph-db-disk0
ceph-deploy osd create --data /dev/sdb --block-db ssd0/ceph-db-disk1
ceph-deploy osd create --data /dev/sdc --block-db ssd0/ceph-db-disk2
--block-wal wasn't used.
If so then BlueFS might eventually overwrite some data at you DB volume
with BlueFS log content. Which most probably makes OSD crash and unable
to restart one day. This is quite random and not very frequent event
which is to some degree dependent from cluster loading. And the period
between actual data corruption and any evidence of this is non-zero most
of the time - we tend to see it mostly when RocksDB was performing
compaction.
So this, if I've understood you correctly, is for those with 3 separate
(DB + WAL + Data) devices per OSD. Not my setup.
Other OSD configuration which might suffer from the issue is main device
+ WAL devices.
Much less failure probability exists for main + DB layout. It requires
almost full DB to get any chances to appear.
This sounds like my setup: 2 separate (DB/WAL combined + Data) devices
per OSD.
Main-only device configurations aren't under the threat as far as I can
tell.
And this is for all-in-one devices that aren't at risk. Understood.
While we're waiting for 14.2.5 to be released, what should 14.2.3/4
users with an at risk setup do in the meantime, if anything?
- Check how full their DB devices are?
- Avoid adding new data/load to the cluster?
- Would deep scrubbing detect any undiscovered corruption?
- Get backups ready to restore? I mean, how bad is this?
Thanks,
Simon.
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