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Benedict commented on CASSANDRA-6696: ------------------------------------- bq. if you lose "data" then you scrub/repair; if you lose metadata you rebuild it from data. You'd always have to do both with any single disk failure. But I agree it isn't optimal; but it is cost-free to maintain. Simply redundantly writing out the metadata would change it to a more uniform process, and tolerant to more than one failure, but at increased cost; at which point you might as well redundantly write out tombstones - either as a bloom filter or an extra sstable. The latter could be complicated to maintain cheaply and safely though. > 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 > 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. > -- This message was sent by Atlassian JIRA (v6.1.5#6160)