Bug 1074632

Description of problem:
Snapshots are generated weekly during scheduled maintenance and when nodes are (un)deployed. A snapshot consists of hard links to SSTable files; consequently, it takes up little disk space. But when an SSTable is deleted during compaction, space will not be reclaimed if the SSTable is included in a snapshot. This can add up over time. There is currently nothing in place for managing snapshots. Here are a few possible options,

1) Move snapshots older than X to a specified location

2) Move all snapshots to a specified location

3) Delete snapshots older than X

4) Move N snapshots (from oldest to youngest) to a specified location

5) Delete N snapshots (from oldest to youngest) to a specified location

This could be done as a reoccurring operation. We could also introduce some new metrics to monitor snapshot disk usage similar to what we already have for the data directories. If the disk usage exceeds a threshold, we can fire an alert and perform one of the above actions. This is another good step we should take for providing storage node disk management.

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