Hello, On Thu, 27 Oct 2016 11:30:29 +0200 Steffen Weißgerber wrote: > > > > >>> Christian Balzer <chibi@xxxxxxx> schrieb am Donnerstag, 27. Oktober 2016 um > 04:07: > > Hi, > > > Hello, > > > > On Wed, 26 Oct 2016 15:40:00 +0000 Ashley Merrick wrote: > > > >> Hello All, > >> > >> Currently running a CEPH cluster connected to KVM via the KRBD and used only > > for this purpose. > >> > >> Is working perfectly fine, however would like to look at increasing / > > helping with random write performance and latency, specially from multiple > > VM's hitting the spinning disks at same time. > >> > > Is it more a question of contention (HDDs being busy) or latency (lots of > > small write I/Os)? > > > >> Currently have journals on SSD so helps with a very short burst, however > > looking into putting some proper SSD "cache" in front. > >> > > You will want to read some of the recent and current "cache tier" threads > > here, especially the "cache tiering deprecated in RHCS 2.0" one, to which > > interestingly there hasn't been a single comment by RH or the devs, > > official or otherwise. > > > > Would the configuration of a seperat SSD only pool with corresponding crush > rules an option to overcome the "cache tier is or will be deprecated" problematic? > Not really, no. A cache-tier can be a very quick band-aid for ALL clients (VMs) w/o any per client configuration and w/o knowledge of client internals. It can also be MUCH more efficient than a dedicated SSD pool in use cases like mine, where the hot objects a) fit nicely in a small space and b) are not in several places, so the only course of action would be to put ALL of the OS disk on a SSD pool. Christian > So that one could use separat SSD based rbd's in qemu vm's like one would > install a mix of disks in a real PC tower (fast SSD for OS startup and datases and > spinning disks for simple file storage). > > [...] > > Regards > > Steffen > > > > > Christian > > > >> 3/ Anything I should be aware of when looking into caching? > >> > >> Thanks for your time!, > >> Ashley > >> _______________________________________________ > >> ceph-users mailing list > >> ceph-users@xxxxxxxxxxxxxx > >> http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com > >> > > > > > > -- > > Christian Balzer Network/Systems Engineer > > chibi@xxxxxxx Global OnLine Japan/Rakuten Communications > > http://www.gol.com/ > > _______________________________________________ > > ceph-users mailing list > > ceph-users@xxxxxxxxxxxxxx > > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com > > -- Christian Balzer Network/Systems Engineer chibi@xxxxxxx Global OnLine Japan/Rakuten Communications http://www.gol.com/ _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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