> Thanks Robert for your response. I'm considering giving SAS 600G 15K a try > before moving to SSD. It should give ~175 IOPS per disk.
> Do you think the performance will be better if i goes with the following > setup ? > 4x OSD nodes > 2x SSD - RAID 1 for OS and Journal > 10x 600G SAS 15K - NO Raid > Two Replication. > According to the IOPS calculation you did for the 4TB. Please clarify is 1100 > IOPS will be for the one node and the cluster IOPS =$number_of_nodes x > $IOPS_per_node ? > If this formula is correct, That's being said the cluster on the 4TB - my > current setup should give in total "2200 IOPS" and the new SAS setup should > give "3500 IOPS" ? > > Please correct me if i understand this wrong. No the current setup is in total 1100 IOPS! You have 44 disks each doing 100 IOPS = 4400 IOPS You have RAID10 which effectively halves the write speed = 2200 IOPS You have a replication factor of 2 in Ceph which halves it again = 1100 IOPS I would not be a fan of a replication factor of 2 with NO raid. Chances that 2 disks in the cluster fail at the same time is significant and you will lose data. Replication of 3 would be the absolute minimum. For the suggested setup that would be: 40 * 175 = 7000 Rep factor of 3 / devide by three = 2300 IOPS So you effectively double the amount of writes you can do. Note that this is the total cluster performance. You will not get this from a single instance since the data would be needed to be written exactly spread across the cluster. In my experience it is "good enough" for some low writes instances but not for write intensive applications like Mysql. Cheers, Robert van Leeuwen
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