Hi,
I have played with stretch clusters a bit but never managed to
un-stretch them fully.
From my experience (using Pacific 16.2.9), once the stretch mode is
enabled, the replicated pools switch to the stretch_rule with size 4,
min_size 2, and require at least one replica in each datacenter.
If one of the two DCs fails, you will still be able to change the crush
rule of your pools back to the traditional replicated rule, and set size
3, min_size 2. After recovery, your objects won't be degraded anymore
and stored 3 replicas in the surviving DC, but the cluster would still
complain about one DC down (with related osds and mons).
It does not seem to exist a 'ceph mon disable_stretch_mode' and the
monmaptool does not implement actions to disable stretch mode and remove
the tiebreaker mon.
I'd be curious to know if it is possible to disable stretch_mode
completely too.
Cheers,
Enrico
On 10/17/22 13:09, Eugen Block wrote:
Hi,
I didn't have the time to play with it yet, but couldn't you just
assign a different ruleset to the pool(s)? Or does ceph complain and
prevent that? I'm not sure if stretch mode will be still active after
changing the crush rule. But I'm not aware that there's a command to
revert this:
$ ceph mon enable_stretch_mode e stretch_rule datacenter
But it does use the "stretch_rule" defined, so maybe additionally
delete that rule? Or start from scratch. ;-)
Regards,
Eugen
Zitat von Manuel Lausch <manuel.lausch@xxxxxxxx>:
Hi,
I am playing around with ceph_stretch_mode and now I have one question:
Is it possible to disable stretchmode again? I didn't found anything
about this in the documentation.
-> Ceph pacific 16.2.9
Manuel
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--
Enrico Bocchi
CERN European Laboratory for Particle Physics
IT - Storage & Data Management - General Storage Services
Mailbox: G20500 - Office: 31-2-010
1211 Genève 23
Switzerland
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