Make sure to check this blog page http://www.sebastien-han.fr/blog/2014/10/10/ceph-how-to-test-if-your-ssd-is-suitable-as-a-journal-device/
Since Im not sure if you are playing arround with CEPH, or plan it for production and good performance. My experience SSD as journal: SSD Samsung 850 PRO = 200 IOPS sustained writes, vs Intel S3500 18.000 IOPS sustained writes - so you understand the difference,,, regards On 30 September 2015 at 11:17, Jiri Kanicky <j...@ganomi.com> wrote: > Thanks to all for responses. Great thread with a lot of info. > > I will go with the 3 partitions on Kingstone SDD for 3 OSDs on each node. > > Thanks > Jiri > > On 30/09/2015 00:38, Lionel Bouton wrote: > >> Hi, >> >> Le 29/09/2015 13:32, Jiri Kanicky a écrit : >> >>> Hi Lionel. >>> >>> Thank you for your reply. In this case I am considering to create >>> separate partitions for each disk on the SSD drive. Would be good to >>> know what is the performance difference, because creating partitions >>> is kind of waste of space. >>> >> The difference is hard to guess : filesystems need more CPU power than >> raw block devices for example, so if you don't have much CPU power this >> can make a significant difference. Filesystems might put more load on >> our storage too (for example ext3/4 with data=journal will at least >> double the disk writes). So there's a lot to consider and nothing will >> be faster for journals than a raw partition. LVM logical volumes come a >> close second behind because usually (if you simply use LVM to create >> your logical volumes and don't try to use anything else like snapshots) >> they don't change access patterns and almost don't need any CPU power. >> >> One more question, is it a good idea to move journal for 3 OSDs to a >>> single SSD considering if SSD fails the whole node with 3 HDDs will be >>> down? >>> >> If your SSDs are working well with Ceph and aren't cheap models dying >> under heavy writes, yes. I use one 200GB DC3710 SSD for 6 7200rpm SATA >> OSDs (using 60GB of it for the 6 journals) and it works very well (they >> were a huge performance boost compared to our previous use of internal >> journals). >> Some SSDs are slower than HDDs for Ceph journals though (there has been >> a lot of discussions on this subject on this mailing list). >> >> Thinking of it, leaving journal on each OSD might be safer, because >>> journal on one disk does not affect other disks (OSDs). Or do you >>> think that having the journal on SSD is better trade off? >>> >> You will put significantly more stress on your HDD leaving journal on >> them and good SSDs are far more robust than HDDs so if you pick Intel DC >> or equivalent SSD for journal your infrastructure might even be more >> robust than one using internal journals (HDDs are dropping like flies >> when you have hundreds of them). There are other components able to take >> down all your OSDs : the disk controller, the CPU, the memory, the power >> supply, ... So adding one robust SSD shouldn't change the overall >> availabilty much (you must check their wear level and choose the models >> according to the amount of writes you want them to support over their >> lifetime though). >> >> The main reason for journals on SSD is performance anyway. If your setup >> is already fast enough without them, I wouldn't try to add SSDs. >> Otherwise, if you can't reach the level of performance needed by adding >> the OSDs already needed for your storage capacity objectives, go SSD. >> >> Best regards, >> >> Lionel >> > > _______________________________________________ > ceph-users mailing list > ceph-users@lists.ceph.com > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com > -- Andrija Panić
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