Re: Ceph benchmarks

[Mark Nelson <mark.nelson@inktank.com>]

On 08/28/2012 03:32 AM, Sébastien Han wrote:
> @Alexandre: I don't have all the machines anymore, I'll see what I can
> do :). Only the commodity cluster remains
>
> @Mark Nelson: 2) Which bench? The RADOS one?
> 3) Sorry the RAID controller doesn't support JBOD...
> 5) I still have the commodity cluster, I'll perform some little rados benchmarks

Ah, that's the problem we have with our H700s.  We do single drive 
raid0s to get around it, but it's not ideal.  Do you have two drives in 
a raid1 or just a single drive?

Some other things we've noticed on our Dell machines:

- Writeback cache is pretty much faster than writethrough cache on all 
of our tests, even sequential writes.
- Concurrent writers to a single raid group seem to tank performance.  I 
still don't know why this is, but it's making buffered IO and any direct 
IO with more than one writer top out at about 95MB/s regardless of the 
number of drives in the raid group.  (And more writers slower 
performance more).

Mark

>
> Cheers!
>
> On Tue, Aug 28, 2012 at 6:27 AM, Mark Kirkwood
> <mark.kirkwood@catalyst.net.nz>  wrote:
>> +1 to that. I've been seeing 4-6 MB/s for 4K writes for 1 OSD with 1 SSD for
>> journal and another for data [1]. Interestingly I did see some nice scaling
>> with 4K random reads: 2-4 MB/s per thread for up to 8 threads (looked like
>> it plateaued thereafter).
>>
>> Cheers
>>
>> Mark
>>
>> [1] FYI not on the box I posted about before - on a more modern pc with
>> 6Bbit/s SATA.
>>
>>
>> On 28/08/12 14:18, Mark Nelson wrote:
>>>
>>> 5) rados bench tests with smaller requests could be interesting on 15k
>>> drives.  I typically see about 1-2MB/s per OSD for 4k requests with 7200rpm
>>> SATA disks.
>>
>>

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