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@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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