Thank you everyone for your replies. We are currently in the process of
selecting new drives for journaling to replace the samsung drives. We're
running our own tests using DD and the command found here :
http://www.sebastien-han.fr/blog/2014/10/10/ceph-how-to-test-if-your-ssd-is-suitable-as-a-journal-device/
dd if=randfile of=/dev/sda bs=4k count=100000 oflag=direct,dsync
I have no trouble believing that this is right, but I was asked to
double-check the command's validity. So, does this command emulate
properly the way ceph journaling write to SSD?
If you want, I can also post the results of our test on different drives
once we're done.
On 4/21/2015 4:04 AM, Andrei Mikhailovsky wrote:
Hi
I have been testing the Samsung 840 Pro (128gb) for quite sometime and
I can also confirm that this drive is unsuitable for osd journal. The
performance and latency that I get from these drives (according to
ceph osd perf) are between 10 - 15 times slower compared to the Intel
520. The Intel 530 drives are also pretty awful. They are meant to be
a replacement of the 520 drives, but the performance is pretty bad.
I have found Intel 520 to be a reasonable drive for performance per
price, for a cluster without a great deal of writes. However they do
not make those anymore.
Otherwise, it seems that the Intel 3600 and 3700 series is a good
performer and has a much longer life expectancy.
Andrei
------------------------------------------------------------------------
*From: *"Eneko Lacunza" <elacu...@binovo.es>
*To: *"J-P Methot" <jpmet...@gtcomm.net>, "Christian Balzer"
<ch...@gol.com>, ceph-users@lists.ceph.com
*Sent: *Tuesday, 21 April, 2015 8:18:20 AM
*Subject: *Re: [ceph-users] Possible improvements for a slow write
speed (excluding independent SSD journals)
Hi,
I'm just writing to you to stress out what others have already said,
because it is very important that you take it very seriously.
On 20/04/15 19:17, J-P Methot wrote:
> On 4/20/2015 11:01 AM, Christian Balzer wrote:
>>
>>> This is similar to another thread running right now, but since our
>>> current setup is completely different from the one described
in the
>>> other thread, I thought it may be better to start a new one.
>>>
>>> We are running Ceph Firefly 0.80.8 (soon to be upgraded to
0.80.9). We
>>> have 6 OSD hosts with 16 OSD each (so a total of 96 OSDs).
Each OSD
>>> is a
>>> Samsung SSD 840 EVO on which I can reach write speeds of
roughly 400
>>> MB/sec, plugged in jbod on a controller that can theoretically
transfer
>>> at 6gb/sec. All of that is linked to openstack compute nodes
on two
>>> bonded 10gbps links (so a max transfer rate of 20 gbps).
>>>
>> I sure as hell hope you're not planning to write all that much
to this
>> cluster.
>> But then again you're worried about write speed, so I guess you do.
>> Those _consumer_ SSDs will be dropping like flies, there are a
number of
>> threads about them here.
>>
>> They also might be of the kind that don't play well with
O_DSYNC, I
>> can't
>> recall for sure right now, check the archives.
>> Consumer SSDs universally tend to slow down quite a bit when not
>> TRIM'ed
>> and/or subjected to prolonged writes, like those generated by a
>> benchmark.
> I see, yes it looks like these SSDs are not the best for the
job. We
> will not change them for now, but if they start failing, we will
> replace them with better ones.
I tried to put a Samsung 840 Pro 256GB in a ceph setup. It is
supposed
to be quite better than the EVO right? It was total crap. No "not the
best for the job". TOTAL CRAP. :)
It can't give any useful write performance for a Ceph OSD. Spec sheet
numbers don't matter for this, they don't work for ceph OSD,
period. And
yes, the drive is fine and works like a charm in workstation
workloads.
I suggest you at least get some intel S3700/S3610 and use them for
the
journal of those samsung drives, I think that could help
performance a lot.
Cheers
Eneko
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