On 2018-03-14T06:57:08, Patrick Donnelly <pdonn...@redhat.com> wrote:
> Yes. But the real outcome is not "no MDS [is] active" but "some or all
> metadata I/O will pause" -- and there is no avoiding that. During an
> MDS upgrade, a standby must take over the MDS being shutdown (and
> upgraded). During takeover, metadata I/O will briefly pause as the
> rank is unavailable. (Specifically, no other rank can obtains locks or
> communicate with the "failed" rank; so metadata I/O will necessarily
> pause until a standby takes over.) Single active vs. multiple active
> upgrade makes little difference in this outcome.
Fair, except that there's no standby MDS at this time in case the update
goes wrong.
> > Is another approach theoretically feasible? Have the updated MDS only go
> > into the incompatible mode once there's a quorum of new ones available,
> > or something?
> I believe so, yes. That option wasn't explored for this patch because
> it was just disambiguating the compatibility flags and the full
> side-effects weren't realized.
Would such a patch be accepted if we ended up pursuing this? Any
suggestions on how to best go about this?
Anything that requires magic sauce on updates beyond the normal "MONs
first, rolling through" makes me twitchy and tends to end with at least
a few customers getting it not quite right ;-)
Regards,
Lars
--
SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284
(AG Nürnberg)
"Experience is the name everyone gives to their mistakes." -- Oscar Wilde
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