Hard Disks for your Desktop PC

Hard drives: SATA vs. SAS

Technology News : Both SATA and SAS drives offer high performance, with transfer rates of 3 gigabits per second. But SAS is full duplex, providing this speed in both directions. That's why SAS drives have differentials of hundreds of dollars for higher capacities.

Some PC makers offer only SATA drives for most of their midrange business models, requiring the purchase of a higher-cost workstation to upgrade to SAS storage.

Our verdict: SATA is fast enough for most business purposes, but if you read and write massive amounts of data, only SAS will meet your needs.

Hard drives: Which flavor of RAID?

When the term RAID was originally coined, the phrase "redundant array of inexpensive disks" was a vision of the putative future. Now, with the price per megabyte in disks astoundingly low, RAID is a superb option for improving both speed and reliability in a desktop machine that has at least two hard-drive bays.

The idea behind RAID is that you pick two targets, one being some combination of redundancy, speed and reliability; the other being the total pool of storage you want to have available. Depending on the manufacturer, the drives you purchase may all have to be of the same capacity, although that's not a strict RAID requirement.

RAID 1, for instance, mirrors all data, writing the same data to each of two drives at the same time. If one drive goes south, the other is fully available. Your total storage capacity is half the total of drive space: two 500GB drives equals 500GB of storage.

RAID 0 stripes data, interleaving blocks to extract more speed out of the hard-drive data transfer system -- that is, you can use two 7,200-rpm drives, but effectively have a far higher speed. RAID 0 offers the full capacity of all drives: Two 500GB drives equals 1TB of capacity.

RAID 5 stripes data and error-correction information across three or more drives. If any one drive dies, the others can reconstruct the missing details, and you lose much less storage than with simple mirroring. With RAID 5 and drives of the same capacity, you lose just the equivalent of a single drive's worth of space in the set. With three 500GB drives, for instance, you have 1TB of storage; with four 500GB drives, you have 1.5TB.

You can combine RAID 0 and RAID 1 as 0+1, which provides both speed and backup, but RAID 5 is usually seen as a superior alternative, even though it can be more costly. It requires at least three drives, but can use many more, and you can expand sets later. If you think you'll want a larger set of storage drives down the road, you need to make sure that your desktop has enough drive bays.

Major desktop PC makers typically include hardware support for RAID 0, 1 and 0+1 even in their less-expensive systems, but for built-in RAID 5 support, you may need to select a higher-priced business workstation; this option typically also requires a hardware RAID card -- costing $650 to $800 -- as well.

That additional cost is partly offset for sets of four or more disks of large capacity compared to RAID 0+1, however, because you drop the cost of drives necessary for the same amount of total storage in RAID 5.

Our verdict: For best use, choosing either RAID 0+1 or RAID 5 makes sense, but RAID 5 clearly provides the best combination of speed and reliability, even at a higher cost.