Hey Mark, Sorry I missed your message as I'm only subscribed to daily digests.
> Date: Tue, 3 May 2016 09:05:02 -0500 > From: Mark Nelson <mnel...@redhat.com> > To: ceph-users@lists.ceph.com > Subject: Re: [ceph-users] Erasure pool performance expectations > Message-ID: <df3de049-a7f9-7f86-3ed3-47079e401...@redhat.com> > Content-Type: text/plain; charset=windows-1252; format=flowed > In addition to what nick said, it's really valuable to watch your cache > tier write behavior during heavy IO. One thing I noticed is you said > you have 2 SSDs for journals and 7 SSDs for data. I thought the hardware recommendations were 1 journal disk per 3 or 4 data disks but I think I might have misunderstood it. Looking at my journal read/writes they seem to be ok though: https://www.dropbox.com/s/er7bei4idd56g4d/Screenshot%202016-05-06%2009.55.30.png?dl=0 However I started running into a lot of slow requests (made a separate thread for those: Diagnosing slow requests) and now I'm hoping these could be related to my journaling setup. > If they are all of > the same type, you're likely bottlenecked by the journal SSDs for > writes, which compounded with the heavy promotions is going to really > hold you back. > What you really want: > 1) (assuming filestore) equal large write throughput between the > journals and data disks. How would one achieve that? > > 2) promotions to be limited by some reasonable fraction of the cache > tier and/or network throughput (say 70%). This is why the > user-configurable promotion throttles were added in jewel. Are these already in the docs somewhere? > > 3) The cache tier to fill up quickly when empty but change slowly once > it's full (ie limiting promotions and evictions). No real way to do > this yet. > Mark Thanks for your thoughts. Peter
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