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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.)
...is the original creator of Linux From Scratch, and therefore registers very high on all standard 7331-meters
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Yes, it does matter. The applications that he tested did not include cpu usage, which are assumed to be neglegable. Try doing an IDE Raid setup while your cpu usage is already high (e.g., a cpu and disk intensive game or running many applications in virtual memory). The simple fact that the scsi controller handles the io operations will cause your performance to increase even more than the article suggests. Now, do you need to spend 500+ dollars to store mp3s and your pron? Probably not.
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Sure it's huge, but I could get just as big of a difference between two runs using the EXACT same hard drive.
The tester didn't even bother to check and see if the files are fragmented, let alone checking to see if the files are on the same part of the disk. The original poster was right, this was NOT in any way a "good" comparison.
If you actually do want a good comparison, head on over to www.storagereview.com. They have compared many different SCSI and IDE drives and have a VERY good grip as to where and when SCSI's performance advantage comes into play.
Here's a quick and easy way to do things: Click on "Performance Database" at the top of the page, and then do a head to head comparison of a bunch of few SCSI drives and a few IDE drives. This will give you a whole whack of benchmarks. What you'll find is that on desktop applications, a 7200rpm IDE can almost always outperform a 7200rpm SCSI drive and is usually about on-par with a 10,000rpm SCSI drive. But, as soon as you get into their server benchmarks, the SCSI drives wipe the floor with the IDE drives.
Then it simply becomes a question of whether you run a server or a desktop. Different drives for different markets.
No. It's NEVER been that way in ATA. Not even the earliest IDE drives. With MFM drives before IDE, and on the Apple ][ and C-64 this sort work was done, but IDE has never been anything like this.
With ATA (a.k.a. IDE), you write 5 bytes to registers to indicate the starting sector number and the number of sectors you want. Then, you write to the command register to transfer control to the drive and it begins working on your command. All modern systems will (usually) issue the "read multiple" command, which instructs the drive to read many sectors into its buffer and give an interrupt when they are all available in the buffer. This isn't something new. The read multiple command has been in the ATA specs for a long time, and PCs have made use of it since at least the days of Windows95 and Linux kernel 1.0. When the drive has all the sectors in its buffer, it asserts the interrupt pin. The read multiple command comes in PIO and DMA flavor, and if you wrote the DMA version to the command register, a DMA operation happens to transfer all those sectors to whereever you set up the DMA controller to store them.
SCSI gets most of its advantage from tagged command queuing and disconnection. These features have appeared in the very latest IDE specs, and so far very few ATA drives support them.
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