Software RAID0+1 using 3 disks

Question

Is it possible to use mdadm to do RAID0+1 using 3 disks? My scenario is 1x2TB disk and 2x1TB disks. Not interested in the RAID0 performance boost, just want to combine them so I can mirror them with the 2TB.

Thanks

EDIT:

I'm thinking this is what I might want to do, if it works:

mdadm --create /dev/md0 --level=0 --raid-devices=2 /dev/sda /dev/sdb
mdadm --create /dev/md1 --level=1 --raid-devices=2 /dev/md0 /dev/sdc

Answer 1

Yes.

You need 4. (At least, with any setup I've seen.) However, you could use 4 partitions, instead of 4 drives. Have one side of the mirror use RAID 0 on two partitions on two 1TB drives. The other side of the mirror could use RAID 0 on two partitions on one 2TB drive. Ought to work.

I don't offhand know how much you'll get of the usual speed benefit of using 2 drives like what RAID 0 often brings. (Actually, I'm rather certain it's implementation-specific. So it might work pretty well, or not.) But 1 drive of 2TB is likely to be a bit slower than 2 drives of 1 TB each, because the single 2TB drive may require reading from a different part of the drive, instead of having two drives reading/writing different spots simultaneously (since they are separate drives).

Is this the best way to do it? Maybe not. (Maybe Server Fault may be a better site for asking such a speed/performance-related question.) However, regarding the question of whether such a thing is doable, I would say, certainly. Just tell the RAID software to work with partitions (rather than drives).