Hi Thoralf,

On 26.02.20 15:35, thoralf schulze wrote:

> recently, we've come across a lot of advice to only use replicated rados
> pools as default- (ie: root-) data pools for cephfs¹.

It should be possible to use an EC pool for CephFS data:

https://docs.ceph.com/docs/master/cephfs/createfs/#using-erasure-coded-pools-with-cephfs

> unfortunately, we either skipped or blatantly ignored this advice while
> creating our cephfs, so our default data pool is an erasure coded one
> with k=2 and m=4, which _should_ be fine availability-wise. could anyone
> elaborate on the impacts regarding the performance of the whole setup?

Apart from the CephFS issue I think EC pools should always have k >= m
as m is the parity part.

> if a migration to a replicated pool is recommend: would a simple
> ceph osd pool set $default_data crush_rule $something_replicated
> 
> suffice, or would you recommend a more elaborated approach, something
> along the lines of taking the cephfs down, copy contents of default_pool
> to default_new, rename default_new default_pool, taking the cephfs up again?

You can only migrate by rsync'ing the data to a complete new CephFS.
There is no inplace migration possible. You also cannot convert a pool
from EC to replicated or vice versa.

Regards
-- 
Robert Sander
Heinlein Support GmbH
Schwedter Str. 8/9b, 10119 Berlin

https://www.heinlein-support.de

Tel: 030 / 405051-43
Fax: 030 / 405051-19

Amtsgericht Berlin-Charlottenburg - HRB 93818 B
Geschäftsführer: Peer Heinlein - Sitz: Berlin

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