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corrected some confusing numbers

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Signed-off-by: Robert Jansen <r.jansen@fairbanks.nl>
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RobertJansen1 2015-01-29 11:03:14 +01:00
parent 94bb265243
commit 4527e8f8eb
1 changed files with 6 additions and 6 deletions
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12
doc/rados/operations/placement-groups.rst
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@ -178,17 +178,17 @@ increased.
No matter how short the recovery time is, there is a chance for a
second OSD to fail while it is in progress. In the 10 OSDs cluster
described above, if any of them fail, then ~8 placement groups
(i.e. ~75 / 9 placement groups being recovered) will only have one
described above, if any of them fail, then ~17 placement groups
(i.e. ~150 / 9 placement groups being recovered) will only have one
surviving copy. And if any of the 8 remaining OSD fail, the last
objects of one placement group are likely to be lost (i.e. ~8 / 8
objects of two placement groups are likely to be lost (i.e. ~17 / 8
placement groups with only one remaining copy being recovered).
When the size of the cluster grows to 20 OSDs, the number of Placement
Groups damaged by the loss of three OSDs drops. The second OSD lost
will degrade ~2 (i.e. ~35 / 19 placement groups being recovered)
instead of ~8 and the third OSD lost will only lose data if it is one
of the two OSDs containing the surviving copy. In other words, if the
will degrade ~4 (i.e. ~75 / 19 placement groups being recovered)
instead of ~17 and the third OSD lost will only lose data if it is one
of the four OSDs containing the surviving copy. In other words, if the
probability of losing one OSD is 0.0001% during the recovery time
frame, it goes from 8 * 0.0001% in the cluster with 10 OSDs to 2 *
0.0001% in the cluster with 20 OSDs.