mon, osd: fix potential collided *Up Set* after PG remapping #20653
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liewegas
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Mar 1, 2018
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A unit test for this would be great: install an invalid mapping and assert that it removes it. Probably in src/test/osd/TestOSDMap.cc? |
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Please add Fixes: http://tracker.ceph.com/issues/23118 to the commit message? |
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The mgr balancer module are basically doing optimizations based on
the snapshots of OSDMap at certain moments, which turns out to be
the culprit of data loss since it can produce bad PG mapping results
sometimes while in upmap mode.
I.e.:
1) original cluster topology:
-5 2.00000 host host-a
0 ssd 1.00000 osd.0 up 1.00000 1.00000
1 ssd 1.00000 osd.1 up 1.00000 1.00000
-7 2.00000 host host-b
2 ssd 1.00000 osd.2 up 1.00000 1.00000
3 ssd 1.00000 osd.3 up 1.00000 1.00000
-9 2.00000 host host-c
4 ssd 1.00000 osd.4 up 1.00000 1.00000
5 ssd 1.00000 osd.5 up 1.00000 1.00000
2) mgr balancer applies optimization for PG 3.f:
pg-upmap-items[3.f : 1->4]
3.f [1 3] + -------------------------> [4 3]
3) osd.3 is out/reweighted etc., original crush mapping of 3.f changed
(while pg-upmap-items did not):
pg-upmap-items[3.f : 1->4]
3.f [1 5] + -------------------------> [4 5]
4) we are now mapping PG 3.f to two OSDs(osd.4 & osd.5) on the same host
(host-c).
Fix the above problem by putting a guard procedure before we can
finally encode these *unsafe* upmap remappings into OSDMap.
If any of them turns out to be inappropriate, we can simply cancel it
since balancer can still re-calculate and re-generate later if necessary.
Fixes: http://tracker.ceph.com/issues/23118
Signed-off-by: xie xingguo <xie.xingguo@zte.com.cn>
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@liewegas All addresed |
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The mgr balancer module are basically doing optimizations based on
the snapshots of OSDMap at certain moments, which turns out to be
the culprit of data loss since it can produce bad PG mapping results
sometimes while in upmap mode.
I.e.:
(while pg-upmap-items did not):
(host-c).
Fix the above problem by putting a guard procedure before we can
finally encode these unsafe upmap remappings into OSDMap.
If any of them turns out to be inappropriate, we can simply cancel it
since balancer can still re-calculate and re-generate later if necessary.
Fixes: http://tracker.ceph.com/issues/23118
Signed-off-by: xie xingguo xie.xingguo@zte.com.cn