Hi,
we recently expanded a ceph cluster with a second site and want to
distribute data accordingly. Two replicate should be present on one
site, one replicate on the other site.
This works well for replicated pools, but not for EC pool, e.g. the RGW
data pool. I've added a second (replicated) storage class to RGW and
moved most of the data to it via lifecycle operations. Now about 670 GB
are left in the EC pool, mostly the head objects which cannot be moved.
I'm looking for the best method to migrate the existing EC pool to a
replicated pool, keeping the downtime a small as possible. So far two
methods seem to be feasible:
1. Cache tiering
Setup cache tiering with the EC pool as frontend pool and a replicated
target pool as backend pool. Set cache mode to proxy and evict all
objects from the EC pool the replicated pool. This will reduce the
downtime to a minimum (stopping all RGW instances, changes the pool name
in the placement definition, restart instance). But I'm not sure whether
a EC pool can acts as frontend pool at all. And cache tiering is
deprecated, so there might be other downfalls.
2. Export / Import
Stop all RGW instances, export the EC pool's content with "rados
export", and import it into the target pool. This should be a safe
method, but will require a significant longer downtime (probably 24+
hours).
Are there any other options? I also evaluated working bucket wise by
creating a second placement set, disable access to a bucket, move all
objects belonging to that bucket from one pool to the other
(identifiable via the bucket's marker), change the placement setting of
the bucket and reenable access. Unfortunately I've didn't found a good
method to temporarily disable bucket access.
Best regards,
Burkhard Linke
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