RAID 0: Hype or blessing?

The RAID-configurations not only do well in most stopwatch trials; they also 'feel' faster, reflecting an increase in the overall responsiveness of the system. When coming from a single Raptor WD740GD to two striped Raptor WD740GDs a sense of relief is noticeable. You get used to it quickly, but stepping back to the single Raptor again confirmed that there is a notable difference; the single Raptor felt 'slower'. Sure, it's still a mighty fast drive on its own, but it doesn't come close to a striped setup. For power users with a well-developed instinct for responsiveness, RAID will deliver. For beginners or less-demanding users who spend more time worrying about getting their printer or dial-up connection to work, the difference might not be noticeable. But then again, that's not the target audience, is it?

The results of a recent poll on the Tweakers.net front page confirm that RAID 0 isn't just a hype. Nearly thirty percent of the responders said they were using a RAID-setup, over fifty percent of which reported major improvements in performance. Thirty percent noted a slight improvement in performance, and only fifteen percent said they hadn't noticed a difference. We realise this isn't a scientifically accurate way to assess the subjective performance of RAID-systems, but it is merely another confirmation of the test results on the previous pages.

	How our users experience RAID (%)
	Big improvement	56,1
	Small improvement	29,4
	No improvement	14,5

RAID and safety

In this article, we discussed several possibilities of RAID 0 considering performance. RAID 0 however has one big disadvantage, namely the increased risk of data loss. If one disk in the array fails, all data is lost. Therefore, we would not advise RAID 0 to anyone who wants to store valuable or important information. Even when you make regular backups, as soon as Murphy does his job you can expect your recent backups to be corrupted as well. By using mirroring in combination with striping (RAID 10), or by using parity (RAID 5), the risk of losing data is greatly reduced. Mind that, especially when using cheap ATA- or SATA-disks, a problem with a drive is certainly not inconceivable. Furthermore, there is always a risk that your RAID-adapter drops a disk in the array. RAID 5, 10 or other levels which provide in redundancy make sure that those incidents can be survived without data loss.

Using RAID 10 does not require you to get some extra hardware. Actually, almost all SATA RAID-adapters with four ports know how to do this. A RAID 5-adapter with some decent performance is a bit more expensive. To eliminate the overhead of parity calculations, fast I/O processors and efficient write-back cache are mandatory. The current generation of SATA RAID-adapters do not perform as well as their SCSI-counterparts at the time of writing, which causes the performance improvement in SATA RAID 5 configurations to be limited.

In the table below, we gathered some of our testing results with SCSI and SATA RAID-adapters. In the RAID 5 category, the MegaRAID SCSI 320-2X puts down the best performance.