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:
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. :)On 4/20/2015 11:01 AM, Christian Balzer wrote: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.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). Wehave 6 OSD hosts with 16 OSD each (so a total of 96 OSDs). Each OSD is aSamsung 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'trecall 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.
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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