Three subsequent checks return three different missing chunks

Hi,

I ran the check command three times within a few minutes. No backups were running in parallel. After the first and the second backup, a prune command ran but did not prune anything due to a “ghost snapshot”.

Each of the three checks reported one missing chunk, but each time it was a different one:

2020-06-28 21:49:15.695 INFO SNAPSHOT_CHECK 11 snapshots and 86 revisions
2020-06-28 21:49:15.701 INFO SNAPSHOT_CHECK Total chunk size is 1114G in 255733 chunks
2020-06-28 21:49:15.995 FATAL DOWNLOAD_CHUNK Chunk a3417ec69ba411e69cacf989ca82592b0d9a22cb97763d33f9aa8c2dc33f5757 can't be found
Chunk a3417ec69ba411e69cacf989ca82592b0d9a22cb97763d33f9aa8c2dc33f5757 can't be found
2020-06-28 22:07:09.292 INFO SNAPSHOT_CHECK 11 snapshots and 86 revisions
2020-06-28 22:07:09.299 INFO SNAPSHOT_CHECK Total chunk size is 1114G in 255733 chunks
2020-06-28 22:07:09.360 FATAL DOWNLOAD_CHUNK Chunk d5cc60ead00091fef23f820dac0b43f0f96926036c3455c4b8862eae3c6b9d9c can't be found
Chunk d5cc60ead00091fef23f820dac0b43f0f96926036c3455c4b8862eae3c6b9d9c can't be found
020-06-28 22:22:14.606 INFO SNAPSHOT_CHECK 11 snapshots and 86 revisions
2020-06-28 22:22:14.612 INFO SNAPSHOT_CHECK Total chunk size is 1114G in 255733 chunks
2020-06-28 22:22:14.847 FATAL DOWNLOAD_CHUNK Chunk 9fde82689a25755d7e17a258e584145ae668a197cb0fe28103ce6ea7f9f8ccc5 can't be found
Chunk 9fde82689a25755d7e17a258e584145ae668a197cb0fe28103ce6ea7f9f8ccc5 can't be found

Is there something severely broken in my backup? Or is this expected behavior?

That is caused by the ghost snapshot. That snapshot should have been deleted for for whatever reason it still exists in the storage but all chunks only referenced by this snapshot should have been turned into fossils.

You can check if this is the case by running duplicacy check -fossils. The -fossils option searches in the fossils if a chunk is missing.

Thanks @gchen, the connection to the ghost snapshot was not clear to me.

I created a check job with -fossils option in Duplicacy Web and got this result:

Running check command from /Users/christoph/.duplicacy-web/repositories/localhost/all
Options: [-log check -storage Backup -fossils -a -tabular]
2020-06-29 08:52:02.627 INFO STORAGE_SET Storage set to some://storage/...
2020-06-29 08:52:04.467 INFO SNAPSHOT_CHECK Listing all chunks
2020-06-29 08:53:12.369 INFO SNAPSHOT_CHECK 11 snapshots and 86 revisions
2020-06-29 08:53:12.377 INFO SNAPSHOT_CHECK Total chunk size is 1114G in 255733 chunks
2020-06-29 08:53:12.450 FATAL DOWNLOAD_CHUNK Chunk ae8c27036ec7f571a1fb7cb40c114e356cf37fc175a63e2d8d056f8e96c80248 can't be found
Chunk ae8c27036ec7f571a1fb7cb40c114e356cf37fc175a63e2d8d056f8e96c80248 can't be found

I’ll guess I have go through the Fix missing chunks steps now, or are fossils different in this regard?

See comment in What is a Ghost Snapshot? Should I start worrying?