Why was fsck priority introduced in /etc/fstab?

Question

Inside the /etc/fstab file, in the sixth column, there is a number that corresponds to whether a filesystem should be scanned for errors. Possible values are:

0 - skip
1 - high priority
2 - low priority

Why was fsck 'priority' introduced in /etc/fstab?

Answer 1

The field exists so you can define the order in which filesystems are checked. Different partitions on the same drive should not be checked at the same time since the IO going to each filesystem will compete with one another, and slow the whole process down. Filesystems on different physical disks could be set to check in the same pass to speed up the whole process since the IO to separate disks would not be competing.

Answer 2

It has to do with boot order. Highest priority is required for booting (/ and in my opinion /usr /var /tmp ...). The /boot filesystem can do with lower priority because by the time the system can start fsck's, it read the necessary files from boot already. Filesystems for home directories etc. are lower priority during boot process.