Hello, Le 03/06/2014 12:14, Christian Balzer a écrit : > A simple way to make 1) and 2) cheaper is to use AMD CPUs, they will do > just fine at half the price with these loads. > If you're that tight on budget, 64GB RAM will do fine, too. I am interested about this specific thought, could you elaborate how did you determine if such hardware (CPU and RAM) will handle well cases where the cluster goes in rebalancing mode when a node or some OSD goes down ?
Because, as Robert stated (and I totally agree with that!), designing a cluster is about the expected performances in optimal conditions, and expected recovery time and nodes loads in non optimal conditions (typically rebalancing), and I found this last point hard to consider and anticipate. As a quick exercise (without taking in consideration FS size overhead ect ...), based on config "1.NG" from Christian (ratio SSD/HDD of 1:3, thus 9x4TB HDD/nodes, 24 nodes) and replication ratio of 2 : - each nodes : ~36TB RAW /~18TB NET - the whole cluster, 864TB RAW / ~432TB NET If a node goes down, ~36TB have to be re balanced between the 23 existing, so ~1,6TB have to be read and write on each nodes. I think this is the expected workload of the cluster in rebalancing mode. So 2 questions : * did my maths are good until now ? * where will be the main bottleneck with such configuration and workload (CPU/IO/RAM/NET) ? how calculate it ? -- Cédric _______________________________________________ ceph-users mailing list ceph-users@lists.ceph.com http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
