RAID system with adaption to changed number of disks

Question

I have to build a RAID 6 with the following 3 requirements:

1. Use different kinds of disks with different sizes.
2. When a disk fails and there's enough space, the RAID should be able to reconstruct itself out of the degraded state. Meaning, if I have e. g. a RAID with 8 disks and 1 fails, I should be able to chose to transform this in a non-degraded (!) RAID with 7 disks.
3. Also the other way round: If I add a disk of what size ever, it should redistribute the data, so that it becomes a RAID with 9 disks.

I don't care, if I have to do it manually.

I don't care so much about speed either.

Is RAIDz capable of doing that? Btrfs, unRAID, SnapRAID or FlexRAID? What RAID system would be able to do that?

Thanks a lot for your help!

Answer 1

Answer regarding ZFS with RAID levels Z1/Z2/Z3:

1. Use different kinds of disks with different sizes.

It is possible, but the usable size of each disk is equal to the smallest disk in the array (I assume it is not what you want). There exists a trick where you partition the disks and use the remaining space for another pool, but it is discouraged for safety reasons and complicates replacement/maintenance.

2. When a disk fails and there's enough space, the RAID should be able to reconstruct itself out of the degraded state. Meaning, if I have e. g. a RAID with 8 disks and 1 fails, I should be able to chose to transform this in a non-degraded (!) RAID with 7 disks.

Not possible, the choice of RAID level is final and can only be changed by destroying and recreating the whole array (losing all data on it in the process). You can run a Z2 or Z3 array in a degraded state (minus one or minus two disks), other than complaining/warning on zpool status, it is no different to having a smaller array.

3. Also the other way round: If I add a disk of what size ever, it should redistribute the data, so that it becomes a RAID with 9 disks.

Not possible, neither adding a disk nor redistribution of already written data is done on ZFS.