[PVE-User] Better understanding CEPH Pool definition

Gregor Burck gregor at aeppelbroe.de
Wed Mar 11 10:57:28 CET 2020


Hi,

I've still problems to understand the pooling definition Size/min in ceph and what it means to us.

We've a 3 node cluster with 4 SSDs (the smallest sinfull setup in the documention).

When I define a ceph pool with 3/2, all implied images requiere the triple storrage.
When I define a ceph pool with 2/1, all implied images requiere the double storrage.

Means the Size/min the quantity of knodes, over wich the data is distributed?

But when I take a knode in maintenance, on the 3/2 setup are still 2 units of each images available, on 2/1 maybe only one.
On a 3/2 setup the filesystem get readonly when 2 nodes are down in the same time, on a 2/1 setup it could be the storage is not available any more?

I try to understand the impact for us, when we set two pools, one with 3/2 for important VMs and one with 2/1 for VMs wich could stand a while off, or 've no claim to be every time up to date or so,....

Bye

Gregor




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