Re: IDE vs SCSI for RAID

["Stephen J. Turnbull" <turnbull@example.com>]

>>>>> "Tobias" == Tobias Diedrich <ranma@example.com> writes:

    Tobias> SCSI is technically superior in that you can attach 15(7)
    Tobias> devices to the host controller and those devices can even
    Tobias> "talk directly with each other" (which is rarely used
    Tobias> AFAIK).

I'm pretty sure that was implemented in my ancient AMI controller;
allegedly you could transfer a file from one drive to another with a
single (fairly complex) command.  Whether linux drivers would do that
I don't know.  It would certainly be useful in applications like
writing CD-Rs etc.

    Tobias> Well the only tuning really needed is setting the
    Tobias> enable_dma option.  (Because that one makes the really big
    Tobias> perceivable difference)

If it's that simple, fine.  But of course it isn't, because you buy
the latest controller and discover that its most advanced modes are
supported in Linux by patches that are still buggy, etc.  Still you
can probably live with that.

    >> The historical answer is "hardware is cheap, wetware is dear."

    Tobias> Hmm, if I have to decide wether to spend x $CURRENCY on a
    Tobias> drive and spend 5minutes to modify my boot scripts to
    Tobias> execute one additional command or 2*x $CURRENCY, then I'm
    Tobias> going for the former.  But of course you have to know
    Tobias> about that first...

As I wrote above, if it's that simple, then IDE really is a cheaper
solution.  The issue I'm concerned with however is _not_ 5 minutes to
modify a boot script _now_.  It's 6-18 months down the road when your
business really starts to ramp up, and suddenly server performance
ramps down and you don't know why.  That's exactly the time that the
admin's value, normally about 1/10 of what he's paid, suddenly goes to
10x what he's paid anyway.  You don't need him analyzing old hardware
decisions, too....


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