WiredTigerPreplog logs missing in the snapshot

I am trying filesystem based snapshot backup for MongoDB. I make a list of files in the dbpath , acquire lock and then take a snapshot and release the lock. I always notice that this file WiredTigerPreplog goes missing in the snapshot when compared to the list of files made before snapshot. Looks like new logs gets created and old ones are deleted, by the time the snapshot is taken. What is this file acctually used for and will this file affect the restore, if it goes missing in the snapshot ?

Thanks in advance,
Akshaya Srinivasan


Please can someone reply to this. I want to know the significance of this wiredtigerprep log, since this goes missing in the snapshot, than the list of files collected before lock is acquired.