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If you make periodic snapshots of a volume, the snapshots are incremental so that only the blocks on the device that have changed since your last snapshot are incrementally saved in the new snapshot. Even though snapshots are saved incrementally, the snapshot deletion process is designed so that you need to retain only the most recent snapshot in order to restore the volume.

http://docs.amazonwebservices.com/AWSEC2/latest/APIReference/ApiReference-query-DeleteSnapshot.html

How to understand, which of snapshots I can remove? Can I remove any? Can I remove first?

Igor Golodnitsky
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Well, the text you qouted is hard to mis-understand: You can delete all snapshots up the newest and will be able to restore your volume from it.

So, if you have 10 snapshots s1 to s10, you can delete all up to s9. If you keep s9 and delete s10, you will only be able to recover to the state the system was at s9.

Sven
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  • How that can be possible? In a moment of deletion, snapshots merged? – Igor Golodnitsky Jan 16 '12 at 10:54
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    It's theoretically easy, yet difficult to explain. Please see http://en.wikipedia.org/wiki/Snapshot_%28computer_storage%29 and the articles linked there for an explanation. – Sven Jan 16 '12 at 11:29