On 11/23/2015 10:42 AM, Eneko Lacunza
wrote:
Hi Mart,
El 23/11/15 a las 10:29, Mart van Santen escribió:
On 11/22/2015 10:01 PM, Robert LeBlanc wrote:
There have been numerous on the mailing
list of the Samsung EVO and
Pros failing far before their expected wear. This is most
likely due
to the 'uncommon' workload of Ceph and the controllers of
those drives
are not really designed to handle the continuous direct sync
writes
that Ceph does. Because of this they can fail without warning
(controller failure rather than MLC failure).
I'm new to the mailinglist and I'm scanning the archive
currently. And I'm getting a sense of the Samsung Evo quality
disks. If i understand correctly, is is at least advise to put
DC grade Journals in front om them to safe them a bit from
failure. For example intel 750's.
I don't think Intel 750's are DC grade. I don't have any of them
though.
OK thx. Interesting, as the 750's are more expansive here than some
Intel S3xxx (per $)
However, is there experience in when the Evo's fail in the Ceph
scenarion? For example, is wear leveling is according SMART
about 40%, it's time to replace your disks? Or is it just
random. Actually we are using mostly Crucial drives (m550,
mx200's), there is not a lot about them on the list. Do other
people use them and what's there experience so far. I expect
about the same quality of the Samsung Evo's, but I'm not sure if
that is the correct conclusion.
My experience with Samsung 840 pro is that they can't be used for
Ceph at all. In case of Crucial M550, they are slow and have
little endurance for ceph use, but I have used them and seemed
reliable during warranty lifetime (we retired them for performance
reasons).
They are indeed not the fasted in the world, but our cluster isn't
that heavy used (max ~4000 IOPS for the whole cluster, ~50 1xTB
disks currently). Disk IO is currently between 5% and 20% usage.
About SSD failure in general, do they normally fail hard, or are
they just getting unbearable slow? We do measure/graph disks
'busy' performance, and use that as an indicator if a disk is
getting slow. Is this is a sensible approach?
Just don't do it. Use DC SSDs, like intel S3xxx, or Samsung DC
Pro, or something like that. You will save a lot of time and
effort, and possibly also money.
It's clear for me the Intel SSDs are the best to go. However, I
still want to estimate at what pace we should replace them in the
future. So it still make sense for us the have some idea of to
predict when it's time to speed up replacements.
Regards,
Mart van Santen
Cheers
Eneko
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