Oh sorry, I had missed that. Indeed that is surprising. Did you read
the recent thread ("SSD IO performance") discussing the relevance of
O_DSYNC performance for the journal?
Cheers, Dan
On Tue, Jun 23, 2015 at 1:54 PM, Jan Schermer <jan@xxxxxxxxxxx> wrote:
> I only use SSDs, which is why I’m so surprised at the CFQ behaviour - the drive can sustain tens of thousand of reads per second, thousands of writes - yet saturating it with reads drops the writes to 10 IOPS - that’s mind boggling to me.
>
> Jan
>
>> On 23 Jun 2015, at 13:43, Dan van der Ster <dan@xxxxxxxxxxxxxx> wrote:
>>
>> On Tue, Jun 23, 2015 at 1:37 PM, Jan Schermer <jan@xxxxxxxxxxx> wrote:
>>> Yes, I use the same drive
>>>
>>> one partition for journal
>>> other for xfs with filestore
>>>
>>> I am seeing slow requests when backfills are occuring - backfills hit the filestore but slow requests are (most probably) writes going to the journal - 10 IOPS is just to few for anything.
>>>
>>>
>>> My Ceph version is dumpling - that explains the integers.
>>> So it’s possible it doesn’t work at all?
>>
>> I thought that bug was fixed. You can check if it worked by using
>> "iotop -b -n1" and looking for threads with the idle priority.
>>
>>> Bad news about the backfills no being in the disk thread, I might have to use deadline after all.
>>
>> If your experience follows the same paths of most users, eventually
>> deep scrubs will cause latency issues and you'll switch back to cfq
>> plus ionicing the disk thread.
>>
>> Are you using Ceph RBD or object storage? If RBD, eventually you'll
>> find that you need to put the journals on an SSD.
>>
>> Cheers, Dan
>
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