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Update DESIGN.md

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gilbertchen
2016-02-23 22:35:57 -05:00
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DESIGN.md
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@@ -49,10 +49,14 @@ The second step, called the *fossil deletion* step, will permanently delete foss
* For each snapshot id, there is a new snapshot that was not seen by the fossil collection step
* The new snapshot must finish after the fossil collection step
![](https://raw.githubusercontent.com/gilbertchen/duplicacy-beta/master/images/fossil_collection_1.png)
The first condition guarantees that if a backup procedure references a chunk before the deletion procedure turns it into a fossil, the reference will be detected in the fossil deletion step which will then turn the fossil back into a normal chunk.
The second condition guarantees that any backup procedure unknown to the fossil deletion step can start only after the fossil collection step finishes. Therefore, if it references a chunk that was identified as fossil in the fossil collection step, it should observe the fossil, not the chunk, so it will upload a new chunk, according to the second fossil access rule.
![](https://raw.githubusercontent.com/gilbertchen/duplicacy-beta/master/images/fossil_collection_2.png)
## Snapshot Format
A snapshot file is a file that the backup procedure uploads to the file storage after it finishes splitting files into