Unlocks a mongod instance to allow writes and reverses the operation of a db.fsyncLock() operation. Typically you will use db.fsyncUnlock() following a database backup operation.

db.fsyncUnlock() is an administrative operation.

Compatibility with WiredTiger

Changed in version 3.2: db.fsyncLock() can ensure that the data files do not change for MongoDB instances using either the MMAPv1 or the WiredTiger storage engines, thus providing consistency for the purposes of creating backups.

In previous MongoDB versions, db.fsyncLock() cannot guarantee a consistent set of files for low-level backups (e.g. via file copy cp, scp, tar) for WiredTiger.