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https://issues.apache.org/jira/browse/CASSANDRA-6696?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13965418#comment-13965418
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Benedict commented on CASSANDRA-6696:
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+1 on dropping separate flush dir. This is a better solution IMO - get full
parallelism of the disks available.
bq. do you mean having a background job move data around after upgrade
Yes, I think this would be preferable. Blocking at startup would make a rolling
upgrade much too painful. If we mark all old sstables as compacting at startup,
we can safely rewrite them in the background, and not worry about them
violating our assumptions/constraints, since they're not eligible for regular
compaction.
> Drive replacement in JBOD can cause data to reappear.
> ------------------------------------------------------
>
> Key: CASSANDRA-6696
> URL: https://issues.apache.org/jira/browse/CASSANDRA-6696
> Project: Cassandra
> Issue Type: Improvement
> Components: Core
> Reporter: sankalp kohli
> Assignee: Marcus Eriksson
> Fix For: 3.0
>
>
> In JBOD, when someone gets a bad drive, the bad drive is replaced with a new
> empty one and repair is run.
> This can cause deleted data to come back in some cases. Also this is true for
> corrupt stables in which we delete the corrupt stable and run repair.
> Here is an example:
> Say we have 3 nodes A,B and C and RF=3 and GC grace=10days.
> row=sankalp col=sankalp is written 20 days back and successfully went to all
> three nodes.
> Then a delete/tombstone was written successfully for the same row column 15
> days back.
> Since this tombstone is more than gc grace, it got compacted in Nodes A and B
> since it got compacted with the actual data. So there is no trace of this row
> column in node A and B.
> Now in node C, say the original data is in drive1 and tombstone is in drive2.
> Compaction has not yet reclaimed the data and tombstone.
> Drive2 becomes corrupt and was replaced with new empty drive.
> Due to the replacement, the tombstone in now gone and row=sankalp col=sankalp
> has come back to life.
> Now after replacing the drive we run repair. This data will be propagated to
> all nodes.
> Note: This is still a problem even if we run repair every gc grace.
>
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