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IDE, SCSI And Recording Everything
Raju writes: "For many years we were told that SCSI is superior to IDE. I always made my systems with SCSI and the others in the household got el-cheapo IDE disks. In the past SCSI beat IDE hands-down but now according to Simson Garfinkel, "today's IDE drives are significantly faster than SCSI drives". In the article at O'Reilly Network he talks about the tests they had run for storage of network data on disks. In the light of this article does anyone see any reason for going with SCSI in a desktop machine? For servers with heavy disk usage patterns it might be different due to command queuing." Disk types aren't what the article's really about, though -- it's a top-level look at network forensics (including advice on building a traffic-analysis system), and makes some interesting points about the unbalanced growth of storage and bandwidth.
As for arrays, beware of the benefits of striping. RAID 0 (striping) has the problem that the more drives you add, the less reliable your array becomes. RAID 0+1 (or RAID 10) mirrors the data as well and keeps your data secure in the event of a single disk failure (and RAID 10 can occassionally suffer multiple disk failures).
On the surface, I would agree with you. However, the planned usage of the disk space in question becomes an important point.
I had this conversation with Greg Oster, a friend from University, who wrote the NetBSD RAIDframe implementation. We were considering setting up a large network server. After doing some number crunching, something became very very very clear: unless we were going to be moving to Gigabit Ethernet, 3 IDE disks in a RAID configuration were going to be more than sufficient to fill our 100MB LAN.
The point is, whether IDE will be "good enough" depends on what you're using it for. For a large fileserver, IDE RAID may well be good enough, depending on you local LAN. For video editting and other purposes where the data is used on the machine where the disks reside, SCSI's command queueing may be the better choice.
Unfortunately, that's not true.
Take a 7200 rpm SCSI drive. Take a 7200 rpm IDE drive. Rip off the electronics.
You now have two identical drives.
That's how it's been for most vendors for years now. SCSI does offer higher speeds (10 and 15k RPM), and the various other benefits spoken of, but reliability is not one of them. The electronics rarely fail on HD's. Instead it's a failure of a mechanical device (the motor, the heads, etc).
SCSI really doesn't serve much purpose on desktop machines anymore. Three times the cost for little or no performance gain. The days of IDE being vastly slower (even on the desktop) are gone, as are the days of IDE CD-R/RW's spitting out coasters if you as much as moved the mouse. There are a few people who will go out and buy the fastest SCSI drives out there, toss them in a RAID array, and then play games on it (no, I'm not kidding... a friend of mine did), but the cost-benefit there is so small as to be ludicrous.
I have a dual P3-850 (was a P2-450). Under heavy CPU load it remains suprisingly responsive. However, if it's under heavy disk load, it crawls, even though Ultra-ATA isn't very heavy on CPU utilisation.
My previous machine was a single PPro-200 with SCSI disks. Under heavy CPU load, it crawled horribly. However, under heavy disk load, it remained much more responsive than my current system.
Therefore I conclude that SCSI really does perform better, even if the drives themselves are matched on throughput and access times. I think most benchmarks suffer a little from tunnel-vision and focus only on the raw disk performance without really taking into consideration what it all means in real world situations.
I put up with the worse overall performance of IDE because it's so much cheaper. Of course, I'm up to my limit (4 devices) and need a new controller if I want to add anymore. And, I have to remember to be careful about tying up the IDE bus attached to my CD-RW when I'm burning discs. I can't see the last point being a problem with SCSI.