Are you talking about global IOPS or per-VM/per-RBD device?
And at what queue depth?
It all comes down to latency. Not sure what the numbers can be on recent 
versions of Ceph and on modern OSes but I doubt it will be <1ms for the OSD 
daemon alone. That gives you 1000 real synchronous IOPS. With higher queue 
depths (or with more RBD devices in parallel) you could reach higher numbers, 
but you need to know what you application needs.
For SATA drives, you need to add their latency to this number, and it scales 
only when the writes are distributed to all the drives (so if you hammer a 4k 
region it will still hit the same drives, even with higher queue depth, which 
might/or might not, increase throughput or even make it worse...)


> On 19 Sep 2016, at 16:23, Matteo Dacrema <> wrote:
> Hi All,
> I’m trying to estimate how many iops ( 4k direct random write )  my ceph 
> cluster should deliver.
> I’ve Journal on SSDs and SATA 7.2k drives for OSD.
> The question is: does journal on SSD increase the number of maximum write 
> iops or I need to consider only the IOPS provided by SATA drives divided by 
> replica count?
> Regards
> M.
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