ceph/ceph — pull request #1855 by kazhang (2014-05-23 00:39:05+00:00)
Title: Update architecture.rst:Calculating PG IDs

To Calculate PG ID, if I didn't get it wrong, CRUSH calculates the hash modulo
the number of PGs instead of OSDs, according to osd/osd_types.cc:963
ceph_stable_mod(pg.ps(), pg_num, pg_num_mask).

Signed-off-by: Kai Zhang