RAID Theory

There are a number of conclusions to draw from our foray into RAID. First and foremost – a RAID is only as good as the workload it’s designed to run. If you’re building an array for high benchmark scores, you’re shooting yourself in the foot for everyday usage. Look at what you want to do with your machine, and build the array to match.

Next, stripe size is your key to tailoring the array to a seek-based or throughput-based workload. Note that every day usage errs on the side of seek, video editing or similar roles err on the side of throughput, and games generally need a little of both.

Speaking of which, for Crysis at least, RAID does bugger all – Oh there’s a performance increase to be had, at best we shaved three seconds off the level load with a three drive array and a 16k stripe, but that’s not much in the grand scheme of your gameplay. You certainly wouldn’t build an array just for this.

For our particular setup, using the onboard NVIDIA controller and Raptor drives, a stripe size of 32k is the sweet spot – but the lesson here is that every machine is different. When you build an array, it’s well worth your time to test the various stripes to see what works best on your configuration, for your workload.

Finally, software RAID outperforms FakeRAID. That said it’s not as simple a choice to disable your RAID BIOS and go all out on software RAID; it’s worth looking at the pros and cons of each.

For example while software RAID performs better, under Windows at least you can’t choose your stripe size (you can under Linux, but we haven’t covered Linux benchmarks here – and yes, we did test some too using Bonnie – as we didn’t have the space).

Next, because software RAID works across partitions, not drives, it’s more flexible than FakeRAID – you can mix and match stripe, mirror, and JBOD (Just a Bunch of Disks) spanned RAIDs across both Windows and Linux as you wish (something Intel calls ‘Matrix Raid’ – nothing new under the sun). And if your drives move to a new machine, they are simply drives with RAIDed partitions and you’ll be able to read data with ease. FakeRAID, on the other hand, is tied to the particular controller, so moving may be harder.

In favour of FakeRAID, however, is that you can install Windows to it as a boot drive, something you can’t do if you’re using Windows software RAID. However, we have a workaround for this which we’ll get onto next.

These are all the issues worth considering when it comes to building your array – and you thought we were going to tell you what to do.

Oh, ok then, try this.


A recommended setup
Let’s say you have four drives ready and waiting to go into a RAID 0 array, just because you can. You could build a four drive RAID-0 array for Windows, your data, and games but this doesn’t really take advantage of parallel I/O. Using RAID 1 would, but you don’t care for redundancy, do you? That’s what backups are for, afterall.

Instead, you could do this: create two two-drive RAID 0 arrays and install Windows on one, and your games and data on the other. You’d be smart and test the arrays as two-drive entities to find the best stripe size for your particular setup. And then once Windows was installed, we’d recommend you do the following: move Program Files to the data array, so that Windows is spread across the two arrays, taking advantage of both striping and (effectively) separate spindles.

This trick works whether you use one, two, three or four drives in a system, in whatever manner you wish to keep drives separate or build arrays.

First copy the entirety of your ‘C:\Program Files’ (and if using x64, ‘Program Files (x86)’) to your data array. Rock back and forth in your chair mumbling something about jelly while you wait. Then fire up Regedit and search for ‘ProgramFiles’ as a Value. When it pops up, edit it and change the path from ‘C:\’ to whatever drive letter you moved it to. Do the same for the ‘Common Files’ value on the same page and, again if you use 64-bit, the (x86) paths as well. Continue to search, and replace all instances.

Don’t have four drives? No worries; even if you have a system with a single Windows boot drive and an array for data, you can still boost Windows performance by moving Program Files across. This would reap better performance than a single three drive array acting as a Windows boot.

Next time we cover RAID it’ll likely be using multiple solid state drives, and at that time we’ll be recommending a change of undies as well as good theory behind the building of an array.