I'm planning on building a new home server and was thinking about the possibility to use disc spanning to create matching disk sizes for a RAID array. I have 2x2TB drives and 4x4TB drives.
Comparison with RAID 5
4 x 4 TB drives
- 1 RAID array
- 12 TB total
4 x 4 TB drives & 2 x 2 TB drives
- 2 RAID arrays
- 14 TB total
5 x 4* TB drives
- Several 4TB disks and 2 smaller disks spanned to produce a 4 TB block device
- 16 TB total
I'm not actually planning on actually doing this because this setup will probably have all kinds of problems, however I do wonder, what would those problems be?
ZFS doesn't really support mismatched disks. In OP's case it would behave as if it was 4x 2TB disks, making 4 TB of raw storage unusable, with 1 disk of parity that would yield 6TB of usable storage. In the future the 2x 2TB disks could be swapped with 4 TB disks, and then ZFS would make use of all the storage, yielding 12 TB of usable storage.
BTRFS handles mismatched disks just fine, however it's RAID5 and RAID6 modes are still partially broken. RAID1 works fine, but results in half the storage being used for parity, so this would again yield a total of 6TB usable with the current disks.