RAID 5, on the other hand, works very well indeed. You need at least three drives and youâ€™ll lose the capacity of one drive to store parity information so if you have three 200GB drives in a RAID 5 array then the array has a capacity of 400GB, but this is proper RAID where you have true redundancy. If any one drive fails then the array will keep on running, and when you replace the failed drive the array will run in reduced performance mode for a couple of hours while the controller rebuilds the array. When that jobâ€™s complete the array is fully restored and itâ€™s all roses in the garden.
RAID 5 takes a fair amount of computing power which requires dedicated hardware. Youâ€™ll find that some manufacturers use a software solution to add RAID 5 to a controller card but this takes loads of clock cycles, so while the HighPoint RocketRaid 1640 card costs less than Â£70 youâ€™ll find that your CPU will run at a 50 per cent load in RAID 5, and thatâ€™s a heavy overhead. By contrast a Promise S150 SX4-M costs nearly Â£200 but CPU usage is less than 15 per cent when running RAID 5.
RAID 5 is on the list of highly desirable features for my next PC, but I canâ€™t help but wonder what the effect will be when the Promise is hammering away at full tilt. I intend to use four WD Raptor 740 drives in the array to give me 200GB of formatted capacity and by my reckoning that will stretch the PCI bus to its limits. The simplest test will be to run some file transfers, perhaps by copying a DVD to the array, while Iâ€™m playing some music. If the sound card doesnâ€™t suffer any pops and clicks then that will be good enough for me, but I have to admit that Mr Doubt is at home.
The alternative is to use an old school server 64-bit/66MHz PCI RAID card, and I have just the thing in the shape of a 3ware 9500S which I could fit in an Asus dual Xeon motherboard that I often use as a test rig.
Thatâ€™s tempting but I think Iâ€™ve recently found an even better solution. Itâ€™s an Areca ARC1220 RAID card which started life as a 64-bit PCI design but which has been updated and now uses a PCI Express 4x interface. Yes, Iâ€™ve actually found a use for the massive bandwidth of PCI Express that isnâ€™t a graphics card. Iâ€™ve even got my hand on a suitable motherboard in the shape of an MSI K8N Diamond which is an SLI design but Iâ€™ve got it set up with one PCI Express graphics card and the Areca RAID card, and itâ€™s really rather good. This could definitely be the basis of my new PC but I rather fear that MSI will want the K8N Diamond back, and that would mess things up terribly. As Mulder and Scully would probably say â€˜The solution is out there, somewhereâ€™.