[rescue] Macs & IDE vs. SCSI

Sat Apr 12 14:06:10 CDT 2003

I usually try to stay out of IDE vs SCSI wars... as I usually try to
stay out of Mac vs PC wars, and occasionaly this unix vs that unis wars....

However, there are a few points I haven't seen anyone mention...

1. IDE drives are only now starting to support tagged command queing type
   features for optimizing access across a busy drive..... this is a
   definate advantage for SCSI drives vs the majority of IDE drives.
2. Most SCSI drives come with 5 year warranty... most IDE drives came with
   2 to 3 year warranties but have not been reduced (with some exceptions)
   to 1 year warranties.
3. SCSI is an internal and external buss.  There is no real external IDE
   buss.
4. More devices can be placed on a SCSI buss (yes, I know this one is
   obvious, but I haven't seen anyone bring it up yet).

I am a SCSI person... but I don't bash IDE.... IDE is a capable interface
and with DMA/UDMA is no longer a processor hog.... but it is IMHO still not
the best interface both in features and versatility.  I think much of what
people have been bashing about busy IDE drives/busses compared to busy
SCSI drives/busses has more to do with the drives... they generally don't
have the kind of features that SCSI drives have as SCSI is generally
built for servers/performance, and IDE is generally for one task single
user systems.

Of course, these are just my observatiosn and opinions.... as always YMMV.

-- Curt

>Date: Sat, 12 Apr 2003 13:43:42 -0400
>From: Phil Stracchino <alaric at caerllewys.net>
>To: The Rescue List <rescue at sunhelp.org>
>Subject: Re: [rescue] Macs & IDE vs. SCSI
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>On Sat, Apr 12, 2003 at 12:55:00PM -0400, Patrick Giagnocavo +1.717.201.3366 
wrote:
>> On Sat, Apr 12, 2003 at 12:32:48PM -0400, Phil Stracchino wrote:
>> > On Sat, Apr 12, 2003 at 06:58:37AM -0700, Lionel Peterson wrote:
>> > Frankly, beyond a certain point, as far as the actual speed of the
>> > drive is concerned it's all moot anyway.  Once you fill (or empty) the
>> > drive's buffer, you're back to the native sustained transfer rate of the
>> > disk mechanism, which is nowhere close to keeping pace with any current
>> > disk interface.
>> 
>> Don't forget protocol overhead as well.
>
>True.
>
>> > Where SCSI's speed advantage comes in is that it supports disconnection,
>> > so it can go off and do something else on another drive while that one
>> > reads more data instead of having to wait for one drive at a time to
>> > finish as on IDE, and that doing so consumes negligible resources on the
>> > host.  On a resource consumption basis, one should think of "IDE disk"
>> > in the same breath as "host-based printer", "winmodem", and unaccelerated
>> > dumb framebuffers.
>> 
>> I agreee on the disconnection speedup but as for "winmodem":
>> 
>> Argh... this is simply not true.  When you are using "UDMA Mode 2" or
>> anything faster or more recent than that, the transfers from disk to
>> CPU are done exactly the same way as a SCSI adapter does it (DMA
>> transfer direct to memory, then 1 interrupt to tell the CPU that data
>> is there).
>
>
>Well, OK, maybe "winmodem" was exaggerating a bit.  Mea culpa.
>
>I stand behind the rest of my points though.
>
>(They make good cover in case of incoming fire.)
>
>
>-- 
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