Merge lp:~james-page/charm-helpers/lp1607961 into lp:charm-helpers

[James Page]

Ensure that a minimum PG count of 2 is used in small OSD configurations with pools with very low weights.

[Liam Young (gnuoy)]

review: Approve

=== modified file 'charmhelpers/contrib/storage/linux/ceph.py'
--- charmhelpers/contrib/storage/linux/ceph.py	2016-07-13 18:56:39 +0000
+++ charmhelpers/contrib/storage/linux/ceph.py	2016-08-02 09:12:06 +0000
@@ -87,6 +87,7 @@
 DEFAULT_PGS_PER_OSD_TARGET = 100
 DEFAULT_POOL_WEIGHT = 10.0
 LEGACY_PG_COUNT = 200
+DEFAULT_MINIMUM_PGS = 2
 
 
 def validator(value, valid_type, valid_range=None):
@@ -266,6 +267,11 @@
         target_pgs_per_osd = config('pgs-per-osd') or DEFAULT_PGS_PER_OSD_TARGET
         num_pg = (target_pgs_per_osd * osd_count * percent_data) // pool_size
 
+        # NOTE: ensure a sane minimum number of PGS otherwise we do get any
+        #       reasonable data distribution in minimal OSD configurations
+        if num_pg < DEFAULT_MINIMUM_PGS:
+            num_pg = DEFAULT_MINIMUM_PGS
+
         # The CRUSH algorithm has a slight optimization for placement groups
         # with powers of 2 so find the nearest power of 2. If the nearest
         # power of 2 is more than 25% below the original value, the next

=== modified file 'tests/contrib/storage/test_linux_ceph.py'
--- tests/contrib/storage/test_linux_ceph.py	2016-07-13 18:56:39 +0000
+++ tests/contrib/storage/test_linux_ceph.py	2016-08-02 09:12:06 +0000
@@ -271,6 +271,13 @@
         pg_num = p.get_pgs(pool_size=3, percent_data=100)
         self.assertEquals(512, pg_num)
 
+        # Test small % weight with minimal OSD count (3)
+        get_osds.return_value = range(1, 3)
+        self.test_config.set('expected-osd-count', None)
+        self.test_config.set('pgs-per-osd', None)
+        pg_num = p.get_pgs(pool_size=3, percent_data=0.1)
+        self.assertEquals(2, pg_num)
+
     @patch.object(ceph_utils, 'get_osds')
     def test_replicated_pool_create_old_ceph(self, get_osds):
         get_osds.return_value = None