> Op 17 juni 2016 om 12:12 schreef Lazuardi Nasution <mrxlazuar...@gmail.com>: > > > Hi Mark, > > What overhead do you mean? Can it be negligible if I use 4KB (extremly, > same with I/O size) stripe/chunk size for making sure that all random I/O > will spreaded through all OSDs? >
Keep in mind that this involves opening additional TCP connections to OSDs. That will come with some overhead. Especially when new connections have to go through the handshake process. I am using 64MB stripes in a case with a customer. They only need sequential writes and reads at high speed. Works great for them. Wido > Anyway, I love coffee too :) > > Best regards, > > > > Date: Thu, 16 Jun 2016 04:01:37 -0500 > > From: Mark Nelson <mnel...@redhat.com> > > To: ceph-users@lists.ceph.com > > Subject: Re: [ceph-users] RBD Stripe/Chunk Size (Order Number) Pros > > Cons > > Message-ID: <c0cbe267-474c-b9e1-b9e6-a4666a764...@redhat.com> > > Content-Type: text/plain; charset=windows-1252; format=flowed > > > > > > > > On 06/16/2016 03:54 AM, Mark Nelson wrote: > > > Hi, > > > > > > larger stripe size (to an extent) will generally improve large > > > sequential read and write performance. > > > > Oops, I should have had my coffee. I missed a sentence here. larger > > strip size will generally improve large sequential read and write > > performance. Smaller stripe size can provide some of the advantages you > > mention below, but there's overhead though. Ok fixed, now back to find > > coffee. :) > > > > > There's overhead though. It > > > means more objects which can slow things down at the filestore level > > > when PG splits occur and also potentially means more inodes fall out of > > > cache, longer syncfs, etc. On the other hand, if using cache tiering, > > > smaller objects means less data to promote which can be a big win for > > > small IO. > > > > > > Basically the answer is that there are pluses and minuses, and the exact > > > behavior will depend on your kernel configuration, hardware, and use > > > case. I think 4MB has been a fairly good default thus far (might change > > > with bluestore), but tuning for a specific use case may mean a smaller > > > or larger size is better. > > > > > > Mark > > > > > > On 06/16/2016 03:20 AM, Lazuardi Nasution wrote: > > >> Hi, > > >> > > >> I'm looking for some pros cons related to RBD stripe/chunk size > > >> indicated by image order number. Default is 4MB (order 22), but > > >> OpenStack use 8MB (order 23) as default. What if we use smaller size > > >> (lower order number), isn't it more chance that image objects is > > >> spreaded through OSDs and cached on OSD nodes RAM? What if we use bigger > > >> size (higher order number), isn't it more chance that image objects is > > >> cached as contiguos blocks and may be have read ahead advantage? Please > > >> give your opnion and reason. > > >> > > >> Best regards, > > > _______________________________________________ > ceph-users mailing list > ceph-users@lists.ceph.com > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com _______________________________________________ ceph-users mailing list ceph-users@lists.ceph.com http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
