As discussed in a previous article (EIDE Drives: Fast Enough for DV?) , if you're looking for a hard drive that's fast enough for DV capturing and editing, look no further than any garden-variety ATA-66 or ATA-100 disk that's available on the market today. Because DV is compressed to a rate that runs at 3.6 MB per second, anything beyond the inexpensive disks commonly available in modern computers is overkill. But after that article hit the Net, many readers asked us to go a step further, explaining the benefits and inner workings of a relatively new technology that borrows from the sheer speed of SCSI -- that is, making an group of EIDE disks work together in a RAID configuration for faster throughput.

What is RAID?
Originally, it was an acronym for Redundant Array of Inexpensive Disks, making two, three or four disks do the work of one. But there is nothing inexpensive about it when you use SCSI or Fibre Channel drives, so the RAID acronym has now come to mean Redundant Array of Independant Drives. But ATA drive technology is putting the Inexpensive back into RAID. Here's where the benefits of EIDE (ATA-66 and ATA-100 are EIDE disks) drives come into play -- instead of spending $400 on one SCSI disk, why not spend that same amount for four 20 GB disks and an EIDE RAID controller and then tie them all together in a RAID 0 configuration? Traditionally, RAID approaches have been expensive because of high prices of SCSI drives and controller cards. But starting in 1997, a new idea came into being. EIDE RAID, because it uses low-cost drives and economical IDE RAID controllers, has made such fast disk systems affordable for home digital video users.

How Do You Set It Up?
Take two, three or four Ultra ATA drives and attach them to an EIDE RAID card or motherboard with its two separate data channels. Via a setup menu, here's where you link the drives together as one drive. EIDE RAID will read and write data simultaneously to all your drives at once.

What's RAID 0, RAID 1 and RAID 5?
RAID 0 (called "striping") combines all the drives in the array as one giant drive, and it doesn't require an even number of drives to work. Actually, RAID 0 isn't really RAID, it's AID, bacause in this configuration, there is no redundancy or data protection. Storage capacity is determined by the smallest drive in the array. That capacity is then applied to format all other drives in the array. For example, if you're using three disks of different sizes, say, 40GB, 60GB, and 75GB drives in a RAID 0 array, your system will see one huge drive of 120GB (40GB x 3) instead of the total of the three (175GB). So, to use RAID 0 in its most efficient way, use same-sized disks. The good news here is that RAID 0 offers 95% better performance under sustained data transfers when one drive per EIDE port is used. So, if that ATA-100 disk you have tops out at 20MB/sec., in a RAID 0 configuration, you'll be pumping an awesome 38 MB/sec. sustained throughput. Wow!

Spanning: If you want to utilize all the capacity of different-sized drives in an array, you may want to "span" the drives. Unfortunately, there are no other benefits except capacity with this spanning concept, but then, when working with DV, keep in mind that even when you're editing real time dual-channel effects, speed of at least 7.2 MB/sec. will keep you from dropping frames. Anything over that will certainly speed up your work, though, allowing you to access your hard disk systems much faster. This is a key concept, especially today, with extremely high speed processors and data busses which can make your disk system a bottleneck that keeps the rest of your computer waiting.

RAID 1 (known as "mirroring") makes and maintains an identical image of data from one drive to a second drive or from multiple drives to a second set of multiple drives. Should one drive fail, like the energizer bunny, its still-running counterpart keeps on going. To the system, the array is still seen as a single drive letter. While RAID 1 is the least efficient use of hard drives, low-cost EIDE makes it practical for trouble-free backup. This can be a quick and transparent way to back up everything you do on your computer -- not a bad idea if you consider that hard drives are not everlasting -- it's not IF they'll fail, but WHEN.

RAID 5 compares data from two drives and calculates a third piece of data called "parity". If one of the drives fails, parity data can be used to rebuild the failed data. Under RAID 5, parity data is stored across all drives in the array. This maximizes the amount of storage capacity available from all drives in the array while still providing data redundancy. RAID 5 also offers the best performance when a redundant (non-RAID 0) configuration is used because you are pulling data from multiple drives.

EIDE RAID allows adding more drives separately from your existing motherboard EIDE ports, giving you greater device flexibility. You're able to boot from your existing controller/drive combination and use your EIDE RAID for dedicated storage -- common for DV editing. Or, you can boot from your EIDE RAID drives and use your onboard controller for more IDE devices. Best of all, mind-boggling speeds can be obtained using EIDE RAID -- in some cases up to 200 MB per second sustained throughput.

If you'd like a hands-on look at EIDE-RAID in action, take a look at this article by DMN's Paulo de Andrade, showing you his experience with a Promise Ultra ATA-100/RAID controller.

Charlie White has been writing about digital video editing since it was the laughingstock of the postproduction industry. He's an Emmy award-winning producer and director for PBS, and Senior Producer at Digital Media Net. Reach him at cwhite@digitalmedianet.com