Wiring up IDE devices

[blu at vl.com (Tom Metro)]

David Kramer wrote:
> I usually wire my IDE chain like:
> 
> IDE0M  Main boot hard drive, software, etc
> IDE0S  Optical drive of some sort
> IDE1M  Second hard drive, mostly data, apache documentroot, tmp, etc
> IDE1S  Optical drive of some sort
> 
> The theory is both hard drives should be on separate channels so they 
> can talk at the same time.

Sounds like a reasonable theory, but what I recall reading about IDE
master/slave pairings is that it is better to pair fast devices
together, as an optical device, which might require a slow IDE mode, can
degrade the performance of a faster device on the same channel.
Accordingly I've always paired my hard drives, and placed optical and
zip drives on the secondary channel.

However, I don't have a lot of confidence in that recollection, and it 
may be based on faulty information. Has anyone else heard similar or 
conflicting information?

Also, given the oddities of IDE and the problems you can occasionally
encounter with certain master/slave pairings, I wouldn't bet on this
behavior being consistent. It probably is affected by which device is
the master as well. Not to mention that the recommendation might have
made assumptions about the IDE driver (such as assuming the behavior of
the Windows IDE driver, which many not be applicable to the Linux IDE
driver).

Conversely, the separate channels theory might similarly fail to provide
a benefit if the IDE controller isn't capable of doing DMA to both
channels at the same time.

Practically speaking, the only way to know would be to benchmark the two
different configurations. Or, if you're really concerned about
performance, buy a SATA controller for your hard drives and use
SATA-to-PATA adapters. That'll also address your cabling complications.

  -Tom