Hi,
If the problem is not severe and you can wait, then according to this:
http://ceph.com/community/new-luminous-pg-overdose-protection/
there is a pg merge feature coming.
Regards,
Denes.
On 12/18/2017 02:18 PM, Jens-U. Mozdzen wrote:
Hi *,
facing the problem to reduce the number of PGs for a pool, I've found
various information and suggestions, but no "definite guide" to handle
pool migration with Ceph 12.2.x. This seems to be a fairly common
problem when having to deal with "teen-age clusters", so consolidated
information would be a real help. I'm willing to start writing things
up, but don't want to duplicate information. So:
Are there any documented "operational procedures" on how to migrate
- an RBD pool (with snapshots created by Openstack)
- a CephFS data pool
- a CephFS metadata pool
to a different volume, in order to be able to utilize pool settings
that cannot be changed on an existing pool?
---
RBD pools: From what I've read, RBD snapshots are "broken" after using
"rados cppool" to move the content of an "RBD pool" to a new pool.
---
CephFS data pool: I know I can add additional pools to a CephFS
instance ("ceph fs add_data_pool"), and have newly created files to be
placed in the new pool ("file layouts"). But according to the docs, a
small amount of metadata is kept in the primary data pool for all
files, so I cannot remove the original pool.
I couldn't identify how CephFS (MDS) identifies it's current data pool
(or "default data pool" in case of multiple pools - the one named in
"ceph fs new"), so "rados cppool"-moving the data to a new pool and
then reconfiguring CephFS to use the new pool (while MDS are stopped,
of course) is not yet an option? And there might be references to the
pool id hiding in CephFS metadata, too, invalidating this approach
altogether.
Of course, dumping the current content of the CephFS to external
storage and recreating the CephFS instance with new pools is a
potential option, but may required a substantial amount of extra
storage ;)
---
CephFS metadata pool: I've not seen any indication of a procedure to
swap metadata pools.
I couldn't identify how CephFS (MDS) identifies it's current metadata
pool, so "rados cppool"-moving the metadata to a new pool and then
reconfiguring CephFS to use the new pool (while MDS are stopped, of
course) is not yet an option?
Of course, dumping the current content of the CephFS to external
storage and recreating the CephFS instance with new pools is a
potential option, but may required a substantial amount of extra
storage ;)
---
http://cephnotes.ksperis.com/blog/2015/04/15/ceph-pool-migration
describes an interesting approach to migrate all pool contents by
making the current pool a cache tier to the new pool and then migrate
the "cache tier content" to the (new) base pool. But I'm not yet able
to judge the approach and will have to conduct tests. Can anyone
already make an educated guess if especially the "snapshot" problem
for RBD pools will be circumvented this way and how CephFS will react
to this approach? This "cache tier" approach, if feasible, would be a
nice way to circumvent downtime and extra space requirements.
Thank you for any ideas, insight and experience you can share!
Regards,
J
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