On 9 January 2014 15:44, Christian Kauhaus <k...@gocept.com> wrote:

> Am 09.01.2014 10:25, schrieb Bradley Kite:
> > 3 servers (quad-core CPU, 16GB RAM), each with 4 SATA 7.2K RPM disks
> (4TB)
> > plus a 160GB SSD.
> > [...]
> > By comparison, a 12-disk RAID5 iscsi SAN is doing ~4000 read iops and
> ~2000
> > iops write (but with 15KRPM SAS disks).
>
> I think that comparing Ceph on 7.2k rpm SATA disks against iSCSI on 15k rpm
> SAS disks is not fair. The random access times of 15k SAS disks are hugely
> better compared to 7.2k SATA disks. What would be far more interesting is
> to
> compare Ceph against iSCSI with identical disks.
>
> Regards
>
> Christian
>
> --
> Dipl.-Inf. Christian Kauhaus <>< · k...@gocept.com · systems administration
> gocept gmbh & co. kg · Forsterstraße 29 · 06112 Halle (Saale) · Germany
> http://gocept.com · tel +49 345 219401-11
> Python, Pyramid, Plone, Zope · consulting, development, hosting, operations
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Hi Christian,

Yes, for a true comparison it would be better but this is the only iscsi
SAN that we have available for testing, so I really only compared against
it to get a "gut feel" for relative performance.

I'm still looking for clues that might indicate why there is such a huge
difference between the read & write rates on the ceph cluster though.

I've been doing some more testing, and the raw random read/write
performance of the individual bcache OSD's is around 1500 iops/second so I
feel I should be getting significantly more from ceph than what I am able
to.

Of course, as soon as bcache stops providing benefits (ie data is pushed
out of the SSD cache) then the raw performance drops to a standard SATA
drive of around 120 IOPS.

Regards
--
Brad.
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