Hi Florent, Journals don’t need to be very big, 5-10GB per OSD would normally be ample. The key is that you get a SSD with high write endurance, this makes the Intel S3700 drives perfect for journal use. In terms of how many OSD’s you can run per SSD, depends purely on how important performance is to you and to a certain extent if you need high sequential bandwidth or high IO throughput. The S3700 SSD will probably give you around 500MB/s sequential bandwidth, which means to get best performance, you wouldn’t want to run more than 5-6 7.2K disks per SSD, as then the SSD would be the bottleneck. If however your workload is mainly random IO, the SSD’s will likely support more disks. But keep in mind that if a SSD fails, then all the OSD’s that it was a journal for will also be lost. If you use 2 SSD’s with a 10-20GB partition in RAID1 for the OS, then you might find you can use the remaining space on the OSD’s (not RAID) split between the 22 disks. Of course keep in mind what I said about IO type and performance. Hope that helps, please let me know if you have any other questions. Nick From: ceph-users [mailto:ceph-users-bounces@xxxxxxxxxxxxxx] On Behalf Of Florent MONTHEL Hi, I’m buying several servers to test CEPH and I would like to configure journal on SSD drives (maybe it’s not necessary for all use cases) Could you help me to identify number of SSD I need (SSD are very expensive and GB price business case killer… ) ? I don’t want to experience SSD bottleneck (some abacus ?). I think I will be with below CONF 2 & 3 CONF 1 DELL 730XC "Low Perf": 10 SATA 7.2K 3.5 4TB + 2 SSD 2.5 » 200GB "intensive write" CONF 2 DELL 730XC « Medium Perf" : 22 SATA 7.2K 2.5 1TB + 2 SSD 2.5 » 200GB "intensive write" CONF 3 DELL 730XC « Medium Perf ++" : 22 SAS 10K 2.5 1TB + 2 SSD 2.5 » 200GB "intensive write" Thanks Florent Monthel |
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