Your mount command doesn't make sense. You are mounting a devtmpfs RAM-based filesystem on /mnt with a name of /dev/sda1. This is not referencing the filesystem on /dev/sda at all.

Perhaps you mean this:

mount /dev/sda1 /mnt
mkdir -p /mnt/home
mount /dev/sda2 /mnt/home

But even this doesn't really make any sense given you're talking about RAID filesystems. If the RAID arrays are built from /dev/sd[abcd]2 and /dev/sd[abcd]3 then you need to refer to the RAID devices /dev/mdX and /dev/mdY (for appropriate values of X and Y).

If you add the output of cat /proc/mdstat to your question it might be possible for me to suggest actual values for X and Y, in which case I'll update my answer for you.

Your mount command doesn't make sense. You are mounting a devtmpfs RAM-based filesystem on /mnt with a name of /dev/sda1. This is not referencing the filesystem on /dev/sda at all.

Perhaps you mean this:

mount /dev/sda1 /mnt
mkdir -p /mnt/home
mount /dev/sda2 /mnt/home

But even this doesn't really make any sense given you're talking about RAID filesystems. If the RAID arrays are built from /dev/sd[abcd]2 or /dev/sd[abcd]3 then you need to refer to the RAID devices /dev/md2 and perhaps /dev/mdY (for some value of Y).