Friday, February 19, 2010

Short Stroke RAID Research

The Short Stroke RAID takes advantage of the fact that data access from the outer edge of a HDD platter is faster than the inner edge. There’s a lot of chatter about it on the Googlenet.

When “Short Stroking RAIDing” we create RAID 0 volumes that leverage a drives outer edge Sweet Spot before the performance drop off.

This snap from HD Tune Pro clearly indicates the performance “sweet spot” for a 250GB WD drive. Looks like it’s about the first 90GB.

As far as I can tell there’s not much more to it than that. I grabbed a couple WD250GB drives and ran them through several tests in different configurations. I consistently measured write speeds at around 150MB/s in all the configurations (I have a feeling OPUS is reporting read speed).

So here are the Read results;

So as you’d expect from the graph 1 Drive runs at 60MB/s two drives striped gives nearly double that (clearly there’s some overhead).

The interesting thing to note is that size of the striped volume made no difference performance as long as the data was in the first 90GB. When we tested “The Rest” at the back end of the disk, things started slowing down, just like in the graph.

The thing is some of the Short Stoking Guides you’ll find online will imply you should only use the outer edge of your disk and not touch the rest. I believe it should be fine to use the rest of the disk as long as it is used for non time critical data, that won’t be accessed when you are using the high performance section of your drive for productivity (IE Gaming), a good candidate for that may be the pr0n folder.

So yeah it’s not a magic bullet. Simply put if you require fast access to data, keep it at the beginning of the drive.

You shouldn’t need to jump through hoops with third party RAID or hard disk management tools (all my testing was with software RAID in Windows).

I recommend putting in some effort to find out what the sweet spot of your drive is, then leverage that with intelligent partitioning. All this “Short Stroking” carry on is pretty much a load of wank!

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