[gpfsug-discuss] Rebalancing with mmrestripefs -P

[valdis.kletnieks at vt.edu]

On Mon, 20 Aug 2018 14:02:05 -0400, "Frederick Stock" said:

> Note you have two additional NSDs in the 33 failure group than you do in
> the 23 failure group.  You may want to change one of those NSDs in failure
> group 33 to be in failure group 23 so you have equal storage space in both
> failure groups.

Keep in mind that the failure groups should be built up based on single points of failure.
In other words, a failure group should consist of disks that will all stay up or all go down on
the same failure (controller, network, whatever).

Looking at the fact that you have 6 disks named 'dNN_george_33' and  8 named 'dNN_cit_33',
it sounds very likely that they are in two different storage arrays, and you should make your
failure groups so they don't span a storage array. In other words, taking a 'cit' disk
and moving it into a 'george' failure group will Do The Wrong Thing, because if you do
data replication, one copy can go onto a 'george' disk, and the other onto a 'cit' disk
that's in the same array as the 'george' disk.  If 'george' fails, you lose access to both
replicas.
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