Hi Rich,
Thank you for your answer. This is good news to hear :)
Regarding the reconfiguration you've done: if I understand correctly, you have
changed it all at once (like download the crush map, edit it - add all the new
OSDs, and upload the new map to the cluster). How did you controlled the impact
of the recovery/refilling operation on your clients' data traffic? What setting
have you used to avoid slow requests?
Kind regards,
Laszlo
On 19.07.2017 17:40, Richard Hesketh wrote:
On 19/07/17 15:14, Laszlo Budai wrote:
Hi David,
Thank you for that reference about CRUSH. It's a nice one.
There I could read about expanding the cluster, but in one of my cases we want
to do more: we want to move from host failure domain to chassis failure domain.
Our concern is: how will ceph behave for those PGs where all the three replicas
currently are in the same chassis? Because in this case according to the new
CRUSH map two replicas are in the wrong place.
Kind regards,
Laszlo
Changing crush rules resulting in PGs being remapped works exactly the same way
as changes in crush weights causing remapped data. The PGs will be remapped in
accordance with the new crushmap/rules and then recovery operations will copy
them over to the new OSDs as usual. Even if a PG is entirely remapped, the OSDs
that were originally hosting it will operate as an acting set and continue to
serve I/O and replicate data until copies on the new OSDs are ready to take
over - ceph won't throw an upset because the acting set doesn't comply with the
crush rules. I have done, for instance, a crush rule change which resulted in
an entire pool being entirely remapped - switching the cephfs metadata pool
from an HDD root to an SSD root rule, so every single PG was moved to a
completely different set of OSDs - and it all continued to work fine while
recovery took place.
Rich
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