> > In the previous email, you are forgetting Raid1 has a write penalty of 2 since it > is mirroring and now we are talking about different types of raid and nothing > really to do about Ceph. One of the main advantages of Ceph is to have data > replicated so you don't have to do Raid to that degree. I am sure there is > math to do this but larger quantity of smaller nodes have better fail-over > than a few large nodes. If you are competing over CPU resources then you > can use Raid0 with minimal write penalty (never thought I suggest Raid0 > haha). You may not max out the drive speed because of CPU but that is the > cost of switching to a data system the machine was not intended for. It > would be good information to know the limits of what a machine could do > with Ceph, so please do share if you do some tests. > > Overall from my understanding it is generally better to move to the ideal > node size for Ceph then slowly deprecate the larger nodes also > fundamentally since replication is done at a higher level than individual > spinners. The idea of doing raid falls farther behind. > The reason for suggesting RAID1 was to ease the job of disk replacement, and also to minimise the chance of crashing. With 1 or 2 OSD's per node and many nodes it doesn't really matter if a screwy disk brings down your system. With 24 OSD's per node, bringing down a node is more of a big deal. Or maybe there is no chance of a failing disk causing an XFS oops these days? (I know it has in the past) Also I think there won't be sufficient network bandwidth to saturate 24 disks so bringing it down to 12 RAID1 sets isn't such a problem. The RAID1 write penalty isn't significant for throughput as the writes are done in parallel, and you can get increased performance on read I think. I don't use RAID1 on my setup, but then I don't have 24-36 disks per node! James _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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