Hands On: Which Raid is right for you?

Raid has long been exploited by servers and workstations to deliver superior disk performance, whether in terms of speed, reliability or a combination of the two. PC enthusiasts have also found Raid a valuable ally.

But with a variety of flavours to choose from, not to mention configuration options, it’s often hard to know whether you’re getting the best from your hardware. Standard benchmarks may not provide an accurate reflection of typical usage.

So this article revisits the eternally popular subject of Raid, explaining the different options and configurations and, crucially, testing them with both pure benchmarks and a popular real-life application.

Test system
To put different Raid configurations to the test I used a PC based on an Intel Core 2 Duo E6700 with 4GB of Ram fitted into an Asus P5W DH Deluxe motherboard.

This booted Vista from a 400GB Seagate hard disk connected to the motherboard’s main controller and used a Promise Supertrak EX8350 controller to host a separate Raid array; this card has since been superseded by the EX8650, which costs a not inconsiderable £250, but for decent hardware-accelerated Raid 5 performance, it’s the way to go.

For the various arrays I used identical Samsung HD501J 500GB disks. As explained in the box on the next page, three disks can offer 1TB of storage in a Raid 5 array, or 1.5TB in Raid 0. Or you could go for Raid 1 – dispensing with one disk as it works with paired disks – for 500GB of storage.

Like most Raid controllers, the EX8350 lets you not only choose the Raid level, but also the stripe size. This refers to the amount of data written to each disk in turn. The EX8350 offers a choice of 32, 64 or 128KB, with 64KB the default. If the data being written is below the stripe size, it will exist on only one disk, losing the performance benefits of being accessed from multiple disks simultaneously.

It’s important to consider the kind of data you’re working with before selecting a stripe size, as you can’t usually change the stripe setting without losing your data and building a new array.

The stripe size is different from the allocation unit size defined by a file system like NTFS. As far as the PC is concerned, a Raid array is exactly the same as a single hard disk: it’s just raw storage waiting to be partitioned and formatted.

So the stripe size only has an impact at the actual hardware level itself, where the controller decides which disks the data will be written to. It doesn’t affect data efficiency, where a small file could find itself wasting potential space by occupying a larger allocated unit size.

To test different stripe sizes, not to mention the different sector sizes also offered by the EX8350, I used the standard HD Tach benchmark from Simpli Software. I also timed how long it took to render a 10-minute AVI file in Adobe Premiere Pro consisting of up to five overlaid video tracks in DV format.