I briefly considered RAID for storage in my new system, but realized that RAID is basically useless as a backup mechanism. Others have made the basic case for why RAID sucks as backup better than I can; I went ahead and ordered a new Caviar Black with the 6 Gb/sec interface as my main drive, and will re-use my older Hitachi for regular internal backup and large video files, torrents etc. Regular Windows backup tool will be enough; I’ll also add a network disk on teh router for network backup of all the machines, and probably get a service like Carbonite for offsite backup.
While researching RAID, though, I became fascinated by the concepty of nested RAID (I had watched Inception twice on a recent flight :). Nested RAID levels are of course nothing new – RAID 1+0 and RAID 0+1 being the most common, giving you advantages of both mirroring and striping for both redundancy and performance.
But what if you nested RAID 0 twice? In other words, four disks, each pair a RAID 0 array, and then those arrays also in RAID 0?
RAID 0 gives you almost double the performance of a single disk (much as SLI gives you almost double the performance of a single GPU), at double the cost (double the drives). Does nesting RAID 0 scale linearly? Would RAID 0+0 give you almost 4x performance at 4x cost?
Triple SLI doesn’t quite give you triple performance, as there is some overhead in coordinating between the cards, In the case of RAID, the overhead is borne by the RAID controllers, however, and theoretically each controller only has to worry about 2 logical units. So I would expect that nesting level 0 RAID arrays would be less burdened by overhead and would be closer to true linear scaling.
Has anyone ever done this? It’s insanely expensive of course – 4 disks, with 4x more risk of drive failure and absolutely no redundancy at all. Though you could envision a RAID 0+0+1 array where you have 4 disks in RAID 0+0 and then do a simple RAID 1 array at the very top with a much larger drive. An example would be to do RAID 0+0+1 with 4 128 GB SSDs and 1 500 GB hard disk. It would be easy to simply reduce the nesting level for performance comparisons, to see how RAID 0+0+1 fares against RAID 0+1, RAID 1+0, RAID 0, and RAID 1 as the baseline.
I don’t have 4 SSDs and a spare 500 GB disk lying around. Or 5 hard drives of any sort, frankly. But I bet the Tom’s folks have the hardware to spare lying around the bench. I’ve posted a forum topic there to see if I can get their attention.
If someone were to spend money on this, though, clearly the best hardware would be four of these Sandforce-based 128 GB drives from ADATA, which basically has all the tech sites swooning. Couple that with a 500 GB WD Caviar Black for the +1 part of the RAID 0+0+1 array and you’d have serious hardware. Total cost for the drives alone would be about $850 as of this posting date, for 500 GB of storage. But if I’m right about the linear scaling, then this would be ridiculously fast.