Lazy umount or Unmounting a busy disk in Linux

Because you're lazy - you want to unmount after the disk operations are done.

Here's a plausible scenario:

You're using rsync to perform your backups and walk away. You can umount -l the drive and once it's finished copying and synched, it unmounts, so that when you come back after a break (that you know will take longer than the backup) you can just unplug the drive instead of having to fiddle with the keyboard again.

This is actually implemented to gain more time to do follow-up tasks in administrative tasks.

If further tasks, independent of this one is waiting in the pipeline, then you can lazy-unmount and go on with others in the batch.

Example: Task 1 and Task 2 are two administrative tasks scheduled back to back.

Task 1 Daily backup

This one copies a large number of files from a project partition to a backup partition, say, /mnt/backupProj, which will be mounted on the fly and unmounted at the end of this task.. The copying takes a significant amount of time.

Task 2 Update SQL-views

Performs a series of database view updates on a dedicated server.

Task 2 is obviously completely independent of Task 1, so we can lazy-unmount /mnt/backupProj without waiting for the backup task to complete.

I use lazy umount in cases where it was obviously stuck for various reasons (such as nfs server down), also when I need to see the original content of the directory that was mounted over by the mount. In both cases the mount is busy. I think there are other edge cases but these 2 are the most common reasons I used the option.