While in theory this should be true, I'm not finding it to be the case for a typical enterprise LSI card with 24 drives attached. We tried a variety of ratios and went back to collocated journals on the spinning drives.
Eagerly awaiting the tiered performance changes to implement a faster tier via SSD. -- Warren On Oct 9, 2013, at 5:52 PM, Kyle Bader <kyle.ba...@gmail.com> wrote: > Journal on SSD should effectively double your throughput because data will > not be written to the same device twice to ensure transactional integrity. > Additionally, by placing the OSD journal on an SSD you should see less > latency, the disk head no longer has to seek back and forth between the > journal and data partitions. For large writes it's not as critical to have a > device that supports high IOPs or throughput because large writes are striped > across many 4MB rados objects, relatively evenly distributed across the > cluster. Small write operations will benefit the most from an OSD data > partition with a writeback cache like btier/flashcache because it can absorbs > an order of magnitude more IOPs and allow a slower spinning device catch up > when there is less activity. > > > On Tue, Oct 8, 2013 at 12:09 AM, Robert van Leeuwen > <robert.vanleeu...@spilgames.com> wrote: >> > I tried putting Flashcache on my spindle OSDs using an Intel SSL and it >> > works great. >> > This is getting me read and write SSD caching instead of just write >> > performance on the journal. >> > It should also allow me to protect the OSD journal on the same drive as >> > the OSD data and still get benefits of SSD caching for writes. >> >> Small note that on Red Hat based distro's + Flashcache + XFS: >> There is a major issue (kernel panics) running xfs + flashcache on a 6.4 >> kernel. (anything higher then 2.6.32-279) >> It should be fixed in kernel 2.6.32-387.el6 which, I assume, will be 6.5 >> which only just entered Beta. >> >> Fore more info, take a look here: >> https://github.com/facebook/flashcache/issues/113 >> >> Since I've hit this issue (thankfully in our dev environment) we are >> slightly less enthusiastic about running flashcache :( >> It also adds a layer of complexity so I would rather just run the journals >> on SSD, at least on Redhat. >> I'm not sure about the performance difference of just journals v.s. >> Flashcache but I'd be happy to read any such comparison :) >> >> Also, if you want to make use of the SSD trim func >> >> P.S. My experience with Flashcache is on Openstack Swift & Nova not Ceph. >> >> >> >> _______________________________________________ >> ceph-users mailing list >> ceph-users@lists.ceph.com >> http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com >> > > > > -- > > Kyle > _______________________________________________ > ceph-users mailing list > ceph-users@lists.ceph.com > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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