The documentation claims that snapshots taken by ops manager are delta (differential) between successive snapshots.

  • How do you then restore?
  • I mean if you are able to delete some snapshots according to retention, how do you connect the dots in between to restore to a point in time.
  • What do they mean by base snapshot? Is that whole backup?
  • How can a given snapshot become full and ready for restore if any snapshot before it is deleted?

I understand one can replay oplog to go forward to a point in time from a given snapshot. This question is if any snapshot before the snapshot where restore begins gets deleted how can you restore?

From MongoDB docs:

"...The snapshot only stores the differences between successive snapshots. Snapshots use only a fraction of the disk space required for full snapshots."

Any help is much appreciated.

  • I deleted my answer as I think it is better described here. Aug 11, 2017 at 1:31
  • I just spoke with mongodb rep and he told me the documentation is wrong and corrected.
    – AAgurmu
    Nov 1, 2017 at 22:31

1 Answer 1


I'm not sure which version of Ops Manager you were running, but there's been a lot of improvements in the last year. The latest docs explain the space-spacing approaches of the different storage choices:

  • MongoDB blockstore and AWS S3 bucket - Each successive snapshot stores only the differences from the previous snapshot. Compression and block-level de-duplication reduce the size of snapshot data.
  • File system store - uses compression only.
  • Hello, Head database is empty. I have OpsManager (4.0.8) running. It has the head database configured, but nothing is getting written in the local backup copy of head database. The Backup agent is running on another node where the replicaset is running. Any input or direction why the backup daemon is not writing anything in the head database,it is empty.
    – Sanjeev
    Mar 20, 2019 at 13:14

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