Building a Digital Video Capture System - Part II

Hard Drives

Probably the most important components of a video capture system are the hard drives.

First, I should mention that I got a lot of emails from people regarding SCSI versus ATA and hard drive speeds (most people said "ATA good, SCSI bad"). Many people pointed out that the current crop of ATA drives have gotten a lot faster in the past few years and that many of them should work just fine for video capture. Okay, I'll give you that one but don't come crying to me if you start dropping frames during capture. A little side note however. Drive manufacturers tend to play fast and loose with their published specifications. They'll use 1,000 instead of 1,024 (which is why a 10 GB drive only holds 9.3 GB). They'll also talk about write transfer rates but sometimes they mean peak transfers in burst mode - writing from the buffer to the platters, not sustained rates from the computer to the platters. If the drive has a 2 MB buffer and you're trying to capture a multi-gigabyte file that buffer isn't going to do you much good.

For example, I checked into the Cheetah X15 which the company claims is 25% faster than any drive they've ever made (it's a 2 GB Fibre Channel or Ultra 160-Wide SCSI LVD drive by the way). Now their press release claims a 69 MB/s rate, their tech specs, however, claim 47.4 MB/s, so that would put their next fastest drive in the 35.5 MB/s range. Not even close to the theoretical bus speeds. Plenty fast for video capture but this just goes to show that just because you have an ATA-100 system doesn't mean you're going to get 100 MB/s. When you start picking through the specs with a skeptical eye you may find that your 66 MB/s drive is really delivering only 25% of that or less. Our standalone review of the RT2500 makes hardware recommendations here , including using two hard drives in your system.

Most capture board companies make these recommendations when choosing hard drives for video capture.

• Get the biggest drive(s) you can afford. You'll quickly run out of storage space when dealing with video - even with a lot of video compression.
• Second, get fast drives. ATA-66 or ATA-100 should work but companies like Matrox still warn that depending on the drive, the bus, and other factors such as buffering and fragmentation you may still drop frames. Matrox recommends drives that can sustain at least 12 MB/s for editing multiple streams but if you're just doing single-stream capture you can get away with half that. Pinnacle recommends a drive that can sustain 10 MB/s and "if you plan on using a DMA capable IDE hard disk (e.g. IDE-UDMA 100 or IDE-UDMA 66) for your video, you should absolutely install a DMA busmaster driver...").
• Most capture card companies will also recommend using a dedicated drive for capture and a separate drive for programs and OS boot.
• Don't use drive compression utilities.
• Finally, they all recommend defragmenting the drive prior to capture.

If you have done all these things and still end up dropping frames then most companies will recommend RAID configurations or (gasp) SCSI drives. If you're serious about video capture and intend to do a lot of it then consider buying a dedicated RAID enclosure (usually RAID 0 unless you really need the security of a more typical RAID configuration). RAID is a way you really can achieve transfer rates approaching the bus maximums. You can do your own RAID configuration and save a few dollars but keep in mind that striping across partitions on the same drive doesn't really buy you any speed.