When I was using MS-DOS not long ago I had a problem where MS-DOS could only use FAT16 drive, which allowed only 2GB partitions. Unfortunately I had to copy files which was 2,6 GB size, and simply couldn't fit in partition, unfortunately for me again all of those files had to be in the same directory/partition.
Today when I was creating my operation system I thought that it is possible that in future someone will run to similar problem.
union filesystem could be represented in unix by mounting two partitions to the same path. Running
ls would show all files on partition 1 as well as on partition 2. In this case also one partition would not require other partition to be able to read all files.
This would solve the problem of 'too small maximum size of partition' which I experienced in MS-DOS with FAT16.
My question is what are the pros and cons of union filesystem?
Thanks to @Hennes who gave me the name of
union filesystem in comment, which allowed me to better sentence the question.
I have no idea how to explain it easier... feel free to edit.