Hi,
On 06/09/2021 08:37, Lokendra Rathour wrote:
Thanks, Mathew for the Update.
The upgrade got failed for some random wired reasons, Checking further
Ceph's status shows that "Ceph health is OK" and times it gives certain
warnings but I think that is ok.
OK...
but what if we see the Version mismatch between the daemons, i.e few
services have upgraded and the remaining could not be upgraded. So in
this state, we do two things:
* Retrying the upgrade activity (to Pacific) - it might work this time.
* Going back to the older Version (Octopus) - is this possible and if
yes then how?
In general downgrades are not supported, so I think continuing with the
upgrade is the best answer.
*Other Query:*
What if the complete cluster goes down, i.e mon crashes other daemon
crashes, can we try to restore the data in OSDs, maybe by reusing the
OSD's in another or new Ceph Cluster or something to save the data.
You will generally have more than 1 mon (typically 3, some people have
5), and as long as a quorum remains, you will still have a working
cluster. If you somehow manage to break all your mons, there is an
emergency procedure for recreating the mon map from an OSD -
https://docs.ceph.com/en/pacific/rados/troubleshooting/troubleshooting-mon/#recovery-using-osds
...but you don't want to end up in that situation!
RADOS typically splits objects across multiple placement groups (and
thus across multiple OSDs); while there are tools to extract data from
OSDs (e.g. https://docs.ceph.com/en/latest/man/8/ceph-objectstore-tool/
), you won't get complete objects this way. Instead, the advice would be
to try and get enough mons back up to get your cluster at least to a
read-only state and then attempt recovery that way.
HTH,
Matthew
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