So many of your questions depends on what your cluster is used for. We don't even know rbd or cephfs from what you said and that still isn't enough to fully answer your questions. I have a much smaller 3 node cluster using Erasure coding for rbds as well as cephfs and it is fine speed-wise for my needs with the cache tier on the hdds. Luminous will remove the need for a cache tier to use Erasure coding if you can wait.
Is your current cluster fast enough for your needs? Is Erasure coding just for additional space? If so, moving to Erasure coding requires you to copy your data from the replicated pool to the EC pool land you will have 2 copies of your data until you feel confident enough to delete the replicated copy. Elaborate on what you mean when you ask how robust EC is, you then referred to replicated as simple. Are you concerned it will add complexity or that it will be lacking features of a replicated pool?
Hi,
Currently, our ceph cluster is all 3-way replicated, and works very
nicely. We're consider the possibility of adding an erasure-coding pool;
which I understand would require a cache tier in front of it to ensure
decent performance.
I am wondering what sort of spec should we be thinking about for the
cache tier, and how robust erasure-coding pools are compared with the
simpler replicated pools?
Our test cluster has 3 storage nodes, each with 60 x 6TB RRD, with NVME
for journals. So for cache tier, we should presumably be thinking SSD?
Roughly how much, and should we consider NVME, or is it not worth the $$$$?
Thanks :)
Matthew
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