Placement Groups : chosing the right pg_num

[Loic Dachary]

Hi Laurent & Mehdi,

I tried to translate our discussions about how to choose the number of placement groups into a revision of the documentation. Here is how it looks at the moment:

https://github.com/dachary/ceph/blob/9177da52f7aa358484f4d9074522da21c9336e49/doc/rados/operations/placement-groups.rst

and the corresponding pull request is at

https://github.com/ceph/ceph/pull/2417

This is a draft and I would very much appreciate your comments. I cc the Ceph development list because it is entirely possible that something significant is missing. Someone knowledgeable will hopefully rectify my mistakes ;-)

Cheers