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Benedict commented on CASSANDRA-6696: ------------------------------------- One possibility here is that we could split bloom filter and metadata onto a separate disk to their data files, so that if/when a disk fails we have the option of scrubbing any records on the remaining disks that we think were present on the lost disk in a file with min_timestamp < gc_grace_seconds ago. Once we've done the scrub (in fact it could probably be "done" instantly by just setting up some filter for compaction + reads until we're fully repaired and have compacted the old data) we can start serving reads again, and can start a repair from the other nodes to receive data for all of the records we're now missing (either through the missing disk or that we're forcefully trashing). > 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: Bug > Reporter: sankalp kohli > Priority: Minor > > 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)