OK forget what I just said
man fstab
<snip>
The fifth field, (fs_freq), is used for these filesystems by the dump(8)
command to determine which filesystems need to be dumped. If the fifth
field is not present, a value of zero is returned and dump will assume
that the filesystem does not need to be dumped.
The sixth field, (fs_passno), is used by the fsck(8) program to determine
the order in which filesystem checks are done at reboot time. The root
filesystem should be specified with a fs_passno of 1, and other filesys-
tems should have a fs_passno of 2. Filesystems within a drive will be
checked sequentially, but filesystems on different drives will be checked
at the same time to utilize parallelism available in the hardware. If the
sixth field is not present or zero, a value of zero is returned and fsck
will assume that the filesystem does not need to be checked.
<snip>