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SCSI vs. IDE In The Real World
An anonymous reader writes "Gerard Beekmans has a really good comparison of the speeds of IDE and SCSI drives up over on devchannel.org. Should help put an end to the myth of IDE erasing SCSI's speed advantage." Note that Beekmans' test handicaps the SCSI disk a bit, with interesting results. (DevChannel, like Slashdot, is part of OSDN.)
a really good comparison of the speeds of IDE and SCSI drives
Oh please. With all due respect to the submitter and Mr. Beekmans, this "comparison" ignores all sorts of other factors: write caching, command overlap, rotational speeds, et al ad nauseum. Yes, some of these are mentioned but a comparison such as this should have hard numbers in a table not opinions. Not that I'm suprised or upset that SCSI trounces IDE, but his comparison is virtually meaningless.
There are many benchmarking suites out there, I'd suggest these be used for the next test to provide some meaningful results.
Trolling is a art,
Negligble? Umm, when you can unpack a kernel in a third of the time and see a 6 and a half minute difference in large reads these performance gains are not negligble. If this was a hairline race that was a matter of a few seconds I could understand, but anyone who does work that is disk intensive will benifit from scsi.
Later,
Phil
In the real world, you must also take into consideration cost. A fair test would be to take a budget of $500 and try two setups, one with IDE and one withSCSI, with any leftover cash spent buying as much RAM as possible. Then see which system perfoms better with a variety of benchmarks.
-- Ed Avis ed@membled.com
He tested a 40gb IDE drive versus a 9gb SCSI drive, both 7200 RPM. The SCSI drive was a lot faster, but this isn't any particular shock; this is pretty old hardware.
:-)
Basically he just told us that circa 2001, SCSI was faster. I think we mostly knew that already.
It would be a lot more interesting to see the test run with one of the 36gb WD Raptors. They are 10K RPM and are *very* fast drives. I use a pair of them striped as RAID 0 in my main desktop; they're faster than anything I've ever used before, including 10KRPM SCSI. (I haven't used 15KRPM SCSI, which I imagine is probably faster still, but very noisy, which is why I went with the Raptors. )
Note also that IDE drives in general are "tuned for desktop usage patterns". I'm not entirely sure what that entails, but I suspect it involves a lot of read-ahead caching; single-user systems tend to be actively reading only one or two things at a time. SCSI is tuned for server performance, and the test of "read lots of small files" is probably much closer to a "server" load than to a "desktop" load.
What I'd like to see is testing of streaming performance in working with really big files. That's something I do fairly frequently. How fast can you extract, say, a 500MB RAR file back to the same disk? How fast is it if you're reading from one and writing to a second? On a personal basis, I do that a lot more than putting 50,000 files in a directory and then reading every single one of them.
However, if I ever DO plan on putting 50,000 files in a directory and then reading all of them on a frequent basis, I'll be sure to choose SCSI.
One would expect the SCSI drives to consistently wallop similarly configured IDE drives (same buffer, spindle, size, #heads and every other physical characteristic you can think of) based solely on one observation: Tagged Command Queuing.
TCQ allows a drive to execute commands out of order to optimize the access pattern. This can have a HUGE impact on performance. Relatively few drives support TCQ on ATA, and very few chipsets support it as well. This is mostly because people who buy ATA aren't *real* performance freaks. They want high streaming performance (like hdparm -tT), but don't know to care about random access performance as it may not be relevant to them.
Server/database access patterns are far more random than typical desktop usage, and this is where SCSI wipes the floor with ATA.
Some have pointed out that RAID enclosures are moving towards IDE drives. This is due to the fact that the integrators are using optimizing logic in the controller to handle emulating TCQ. So you can have a stone-dumb drive in there and it doesn't matter as long as the physicals are there.
SCSI drives also typically come with caching algorithms which are intended to try to increase cache hits by using more intelligent cache allocation and predictive reading.
Combine that with better, more intelligent controllers, command detachment, and infinitely better bus sharing - and SCSI cannot be compared to ATA in high demand situations.