> Of course -- the mons can't tell the difference!
That is really unfortunate, it would be nice to know if the filesystem has been degraded and to what degree.
Ok but what if you have your standby go down and a master go down. This could happen in the real world and is a valid error scenario. Also there is a period between when the standby becomes active what happens in-between that time?
> It depends(tm) on how the metadata is distributed and what locks are
held by each MDS.Your saying depending on which mds had a lock on a resource it will block that particular POSIX operation? Can you clarify a little bit?
> Standbys are not optional in any production cluster.
Of course in production I would hope people have standbys but in theory there is no enforcement in Ceph for this other than a warning. So when you say not optional that is not exactly true it will still run.
On Thu, Apr 26, 2018 at 3:37 PM Patrick Donnelly <pdonnell@xxxxxxxxxx> wrote:
On Thu, Apr 26, 2018 at 3:16 PM, Scottix <scottix@xxxxxxxxx> wrote:
> Updated to 12.2.5
>
> We are starting to test multi_mds cephfs and we are going through some
> failure scenarios in our test cluster.
>
> We are simulating a power failure to one machine and we are getting mixed
> results of what happens to the file system.
>
> This is the status of the mds once we simulate the power loss considering
> there are no more standbys.
>
> mds: cephfs-2/2/2 up
> {0=CephDeploy100=up:active,1=TigoMDS100=up:active(laggy or crashed)}
>
> 1. It is a little unclear if it is laggy or really is down, using this line
> alone.
Of course -- the mons can't tell the difference!
> 2. The first time we lost total access to ceph folder and just blocked i/o
You must have standbys for high availability. This is the docs.
> 3. One time we were still able to access ceph folder and everything seems to
> be running.
It depends(tm) on how the metadata is distributed and what locks are
held by each MDS.
Standbys are not optional in any production cluster.
--
Patrick Donnelly
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