The Storage Review recently ran a feature on the Seagate Barracuda 36 series, Seagate’s current economy-class SCSI drive. Like many low-end Seagate SCSI drives of the past, it is a converted ATA/IDE design. And Storage Review eats these kinds of units up, because theoretically they provide a nice way to demonstrate the difference between IDE and SCSI.
The result? The SCSI unit was actually slower than its IDE brethren in some of the tests.
The conclusion? SCSI isn’t necessarily faster than IDE.
That’s partially right. Taking the same drive mechanism and replacing the IDE circuitry with SCSI circuitry won’t result in a rockin’-fast drive. SCSI does have more overhead than IDE, so without some other changes, the drive won’t be an impressive performer.
The thing is, people don’t buy expensive SCSI controllers and then put retreaded IDE drives on them. Or at least they shouldn’t. The Barracuda 36 series is intended for people replacing SCSI drives in older equipment. Since the drive will frequently be replacing a five-year-old drive (or older), it doesn’t have to be a screamer. Anything made today will be faster than anything you can find from the mid-90s.
SCSI gives other advantages over IDE. First, with a modern host adapter (don’t call it a controller; you’ll get dirty looks) you can connect 14 devices and only use one interrupt. On today’s crowded PCs that try to be everything to everyone, that can be a real boon. Second, you have far fewer limitations over cable length. Don’t buy an IDE cable longer than 18 inches; you’re just asking for trouble. I know, I know, some of you have 36-inch IDE cables and they work fine. Trust me: Replace it with a shorty, and you’ll get fewer data errors, which means a more reliable system at the very least, and possibly a faster system as well due to fewer retransmissions. With SCSI, you can actually use the top bays in that five-foot-tall megatower you bought. Third, you can get external SCSI devices, in the event that you made the mistake of not buying that five-foot-tall megatower, or if you just like portability. This is less of a factor in these days of Firewire and USB 2.0, but it’s still a nicety you don’t get with IDE. Fourth and most importantly, SCSI devices sharing the same bus can talk at the same time. When you put two IDE drives on the same channel, one drive has to wait for the other to shut up before it can speak its peace. This limits the advantage of having multiple drives. With multiple SCSI drives, you can actually saturate all that bandwidth you paid for.
The fifth advantage of may soon fade: command queuing. SCSI drives don’t have to perform requests in the order received. If you’re constantly accessing two files at once, reading one, then writing to the other, in alternating fashion, the IDE drive will be jumping all over the place. The SCSI drive will figure out how to reorder those requests so it doesn’t have to jump around as much. IBM’s recent Deskstar drives can do command queuing as well, provided the operating system supports that mode of operation. But it’s not a common feature in IDE drives yet. This advantage usually won’t show up in benchmarks, but it’s significant. SCSI drives, to use a popular middle-management buzzword, work smarter. If you’ve got a Windows 2000 or XP system with a SCSI drive in it, try using the system while defragmenting the drive. The system will be slower, but not unusable. That’s never true of an IDE drive.
And the sixth advantage of SCSI doesn’t really have much to do with SCSI. With SCSI, you get cutting-edge technologies first. You can’t buy a 15K RPM IDE drive. You can’t even buy a 10K RPM IDE drive. There’s only one IDE drive on the market with an 8-meg cache on it. Caches that size are commonplace on contemporary SCSI drives, and the gargantuan Seagate Barracuda 180 has a 16-meg cache. It also costs as much as a nice computer all by itself, so it’s not exactly a consumer-class drive, but it’s available if you’ve got more money than patience.
Benchmarks are deceiving. Some changes will double the benchmark scores, but a user won’t tell much difference. Other changes barely register, but the user notices them. SCSI is one of those, especially if you multitask a lot.
It’s true that there’s no point in spending $400-$500 for a disk subsystem in a PC you use for word processing and e-mail. You’ll notice a difference, but it’s not worth the extra cost. Although if you’re buying a used system and have a choice between a system with IDE disks and SCSI disks, you should get the SCSI system, even if it means ponying up another 50 bucks. You’ll thank yourself for it.
As for me, I love my SCSI systems with 10K RPM drives in them. They’re wicked fast, and no louder than the IDE drives of four or five years ago. (I don’t have a current IDE drive to compare them to.) I can let my e-mail inbox fill up with thousands of messages without it dragging beyond belief, and my non-Adobe applications load in less than three seconds. Most of them load in less than a second. The drives themselves are small and expensive, but you’re buying performance, not capacity. I can’t fill up a 9-gig drive with applications anyway. Neither can most people.
So no, SCSI isn’t a magic silver bullet. But that doesn’t mean it’s not worth having.