Hi David,
What is your min_size in the cache pool? If your min_size is 2, then the
cluster would block requests to that pool due to it having too few copies
available.
this is a little embarassing, but it seems it was the min_size indeed.
I had changed this setting a couple of weeks ago, but as I found out,
a colleague had to rebuild the cache pool. And since we have defined
the default min_size of 2 for new pools in our ceph.conf my changes
were overwritten, of course.
A little test where I stopped one of the two SSDs after changing
min_size back to 1 was successful, I don't see any hints for slow
requests, also no co-worker complained about hanging VMs :-)
Thanks for pointing that out (again), I'll try to convince my employer
to get a third SSD ;-)
Regards,
Eugen
Zitat von David Turner <drakonstein@xxxxxxxxx>:
PPS - or min_size 1 in production
On Wed, Nov 1, 2017 at 10:08 AM David Turner <drakonstein@xxxxxxxxx> wrote:
What is your min_size in the cache pool? If your min_size is 2, then the
cluster would block requests to that pool due to it having too few copies
available.
PS - Please don't consider using rep_size 2 in production.
On Wed, Nov 1, 2017 at 5:14 AM Eugen Block <eblock@xxxxxx> wrote:
Hi experts,
we have upgraded our cluster to Luminous successfully, no big issues
so far. We are also testing cache tier with only 2 SSDs (we know it's
not recommended), and there's one issue to be resolved:
Evertime we have to restart the cache OSDs we get slow requests with
impacts on our client VMs. We never restart both SSDs at the same
time, of course, so we are wondering why the slow requests? What
exactly is happening with a replication size of 2? We assumed that if
one SSD is restarted the data is still available on the other disc, we
didn't expect any problems. But this occurs everytime we have to
restart them. Can anyone explain what is going on there? We could use
your expertise on this :-)
Best regards,
Eugen
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Eugen Block voice : +49-40-559 51 75
NDE Netzdesign und -entwicklung AG fax : +49-40-559 51 77
Postfach 61 03 15
D-22423 Hamburg e-mail : eblock@xxxxxx
Vorsitzende des Aufsichtsrates: Angelika Mozdzen
Sitz und Registergericht: Hamburg, HRB 90934
Vorstand: Jens-U. Mozdzen
USt-IdNr. DE 814 013 983
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