None of your RGW pools would require a cache tier. Your volumes for OpenStack would need a cache tier. I use Erasure Coding for my data volumes in VMs as well as for CephFS. I don't use Erasure Coding for system volumes in VMs. I wanted to avoid the increased latency that would impose onto the VMs.
For your RGW pools, though, RGW can handle EC natively without any additional cache tiers. If I were you, I would create some new pools for EC and create test VMs to see how well they perform in comparison to their replica counterparts. You would need to have both pools up at the same time anyway to migrate the volumes between replica to EC anyway, so you might as well set it up and test with it.
On Tue, Jul 11, 2017 at 11:32 AM Matthew Vernon <mv3@xxxxxxxxxxxx> wrote:
Hi,
On 07/07/17 13:03, David Turner wrote:
> 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.
Sorry; our cluster is used partly to provide volumes for OpenStack, and
party for S3 (via rgw).
> 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?
I think our cluster is currently fast enough (I'm sure our users would
always want more speed :) ); we were thinking that erasure coding would
save us some disk space, yes.
I'm concerned that erasure coded pools (and a cache tier in front of
them) will be a more complex setup to manage (we use ceph-ansible) than
our current setup (replicated pools).
Thanks,
Matthew
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