Possible reasons:

  1. Deletes aren’t being forwarded.
    There is an option in the Vault / Replication settings - check the Web Admin / Admin tool to see if deletes are being forwarded on the replication settings.

  2. Deletes are being forwarded, but haven’t yet been forwarded. This could be due to:
    1. a large number of objects have recently been written/deleted and all the changes haven’t been forwarded yet
    2. the communication pipe is too small for the amount of data being written
    3. the replication task is paused (check admin)
    4. replication task is set to run in a time window (check admin tool)

  3. Small differences can come from the MatrixStore system files - small files that are used for admin purposes - the destination vault could have more of these than the source vault.

  4. Someone has directly added a number of objects at the destination cluster, or the vault is used as a destination from more than just one source vault.

  5. The destination cluster could have a number of deleted files in its trash can.

  6. The destination cluster could have orphaned objects - objects that were written from the source cluster but were never indexed (e.g. replication stopped for some reason before the new object could be indexed).

  7. The destination cluster may have proxy generation enabled.