Feasible to have a RAID of RAIDs

Question

Having a RAID can increase speeds and redundancy.

Can a RAID be made using other RAIDs as "disks"? This could further increase performance and redundancy. How many levels can you go?

Answer 1

This is a standard practice and is called nesting. Raid 10 is an example. There are many benefits depending on how you set it up. Here's the wiki to get you started.

http://en.wikipedia.org/wiki/Nested_RAID_levels

Answer 2

A RAID of RAIDS is not at all exotic: The two-digit RAID levels (e.g. 10, 50, 55) are routinely constructed as just that, e.g. a RAID 10 is nothing elese than a RAID0 consisting of members, which themselves are RAID1 constructs.

Answer 3

Ill format this later... There is a limit to how much performance you can get. The best write IOPs you can get is with RAID0 that's also the most size. All raid types modify write iops by 0 to 1 ratio, this is called the write penalty (really its the inverse of this number). It can't be more. Max Read iops are just number of drives * IOPs, also this is the max write iops you can get which you would need to raid0 everything. More raids on top more penalty for write. Read iops always stays the same. However for each layer you get docked down performance for an extra layer. Raid 0 is 1 write penalty so it Doesnt affect that number. Raid 5 is 4. Raid 6 is 6. Raid 1 is 2 (or number of drives in the mirror - 99% of the time its 2 so that number is 2). Raid 10 has write penalty of 2 (that means u have a bunch of raid1s all connected as a raid 0), the lowest one. Raid 50 would be a write penalty of x/4. Where x is the number of raids 5s that you have that are all wrapped as a raid 0. The best nested raids for performance and size are Raid10,50,60. For example raid 55 would have a write penalty of x/16 where x is the number of raid 5s (number of vdevs)... I'll clear this up later basically best performance is raid0 or raid10. More nesting and you get less write iops. Read iops are unaffected by all of this.