Hi Matthew,
There is a possibility related to your point #4 if your cluster has some
extra space (there's probably a way to count what would be needed
depending on the EC profile you use).
I would :
1/ create the new EC pool => it corresponds to the RGW data pool only
2/ create EC Ruleset associated to the pool
3/ Change the current RGW data pool from using the former replica
ruleset to the new EC ruleset.
That way there is no downtime and Ceph will migrate all the data itself
from one pool to the other by rebalancing them.
You will however tweak the backfill parameter to go faster/slower
depending on the impact on the clients.
You can always come back to previous configuration by re-associating the
old ruleset to the RGW data pool.
With Regards,
Eric.
On 12/4/18 6:33 PM, Matthew Vernon wrote:
Hi,
We're planning the move of our production Ceph cluster to Luminous
(from Jewel), and thinking about migrating the main S3/radosgw pool to
erasure-coding.
It's quite large (1.4PB / 440 M objects).
I've seen
http://cephnotes.ksperis.com/blog/2015/04/15/ceph-pool-migration/
which seems to be the standard set of options:
1) rados cppool
This would require a lot of downtime (since it just copies objects
one-by-one without checking if the object is already in the target
pool), and I don't know if the warning means this would break things
anyway:
WARNING: pool copy does not preserve user_version, which some apps may
rely on.
2) making a new pool as a cache tier
This looks pretty risky to me (and easy to get wrong), and I imagine
the cache-flush-evict-all stage is very IO intensive. Has anyone tried
it with a large pool?
3) Rados export/import
I think this has the same problem as 1) above - having to do it as a
big bang, and needing a lot of temporary storage
4) make a new pool, make it the default for rgw [not in above link]
This would, I think, mean that new uploads would go into the new pool,
and would be non-disruptive. But, AFAICS, there is no way to:
i) look at what % of a users' buckets/objects are in which pool
ii) migrate objects from old to new pool
The second is the kicker, really - it'd be very useful to be able to
move objects without having to download, remove, re-upload, but I
don't think there's an API to do this? Presumably you could hack
something up based on the internals of the radosgw itself, but that
seems ... brave?
Surely we're not the only people to have wanted to do this; what have
others done?
Regards,
Matthew
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