Raid 01

[BTRY B 529th FA BN]

I have a question that about RAID 01. In wiki it says: "RAID 0+1 (or 01) is a striped data set (RAID 0) which is then mirrored (RAID 1). A RAID 0+1 array requires a minimum of four drives: two to hold the striped data, plus another two to mirror the first pair."

Could the RAID 0 just be used in a RAID 1 for a drive total of 3 drives instead? If so, what then is that called? Still RAID 01?

e.g. Two drives stripped to get 1 logical drive, then the logical drive would then be mirrored by a software app to a drive the same size (500g + 500g mirrored to a 1tb drive) thus creating a backup of the RAID 0 set and only using 3 drives.

EDIT: this would create a problem if the 1tb drive was active all the time but if it weren't actually plugged in via the psu this would be a fail safe operation

 

[MerlinRML]

The point of RAID 0+1 is that the RAID controller is aware of all 4 disks and writes the data at the same time to all 4 of them. It provides the performance of a 2-disk RAID0 set, but still mirrors that data to a second set of disks for redundancy.

Your solution is similar but not the same. It would probably require 2 different RAID solutions that are unaware of each other which adds even more complexity than RAID already does. It's like using software RAID on top of hardware RAID. People do it, but it's generally frowned upon because if it ever fails you pretty much have to involve multiple RAID vendors and it becomes a complete clusterf*.

In your case, you would have a 2 drive RAID0 mirroring to a single drive. The lowest common denominator, your single drive, will slow the RAID0 down. It would probaby negate any performance gain and basically invalidate the whole point of doing the RAID0 in the first place.

You would still have redundancy, but because you have 2 different solutions, you'll do a RAID0 write, then after it completes, it'll do a RAID1 mirror. it's not quite as good as a RAID0+1, but this is really splitting hairs and is going to probably not matter.

So, with all that said explaining how it will work, you're probably better off just doing a RAID0 + backup. Schedule your backups more frequently and you can close your window of potential data loss due to RAID failure to hours or minutes pretty easily.