[Pkg-ceph-commits] [ceph] 01/01: Add NEWS entry about CRUSH issues fixed in 0.80.9

[Gaudenz Steinlin]

This is an automated email from the git hooks/post-receive script.

gaudenz pushed a commit to branch master
in repository ceph.

commit 70fc1ddd3b097d26ce9ab8cf29f085c1675dfa76
Author: Gaudenz Steinlin <gaudenz at debian.org>
Date:   Mon May 4 22:59:18 2015 +0200

    Add NEWS entry about CRUSH issues fixed in 0.80.9
---
 debian/NEWS | 42 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 42 insertions(+)

diff --git a/debian/NEWS b/debian/NEWS
new file mode 100644
index 0000000..d1bb788
--- /dev/null
+++ b/debian/NEWS
@@ -0,0 +1,42 @@
+ceph (0.80.9-2) unstable; urgency=medium
+
+  The 0.80.9 point release fixes several issues with CRUSH that trigger excessive
+  data migration when adjusting OSD weights. These are most obvious when a very
+  small weight change (e.g., a change from 0 to .01) triggers a large amount of
+  movement, but the same set of bugs can also lead to excessive (though less
+  noticeable) movement in other cases.
+
+  However, because the bug may already have affected your cluster, fixing it
+  may trigger movement back to the more correct location. For this reason, you
+  must manually opt-in to the fixed behavior.
+
+  In order to set the new tunable to correct the behavior:
+
+      ceph osd crush set-tunable straw_calc_version 1
+
+  Note that this change will have no immediate effect. However, from this
+  point forward, any ‘straw’ bucket in your CRUSH map that is adjusted will get
+  non-buggy internal weights, and that transition may trigger some rebalancing.
+
+  You can estimate how much rebalancing will eventually be necessary on your
+  cluster with:
+
+      ceph osd getcrushmap -o /tmp/cm
+      crushtool -i /tmp/cm --num-rep 3 --test --show-mappings > /tmp/a 2>&1
+      crushtool -i /tmp/cm --set-straw-calc-version 1 -o /tmp/cm2
+      crushtool -i /tmp/cm2 --reweight -o /tmp/cm2
+      crushtool -i /tmp/cm2 --num-rep 3 --test --show-mappings > /tmp/b 2>&1
+      wc -l /tmp/a                          # num total mappings
+      diff -u /tmp/a /tmp/b | grep -c ^+    # num changed mappings
+
+  Divide the total number of lines in /tmp/a with the number of lines
+  changed.  We've found that most clusters are under 10%.
+
+  You can force all of this rebalancing to happen at once with:
+
+      ceph osd crush reweight-all
+
+  Otherwise, it will happen at some unknown point in the future when
+  CRUSH weights are next adjusted.
+
+ -- Gaudenz Steinlin <gaudenz at debian.org>  Mon, 04 May 2015 22:49:48 +0200

-- 
Alioth's /usr/local/bin/git-commit-notice on /srv/git.debian.org/git/pkg-ceph/ceph.git