[SunRescue] Ahh the old SCSI vs IDE thing, was Re: HBA's

[Chris Byrne]

Eric Ozrelic wrote:
> 
> I've seen bare bones U30's go for around $750 on eBay, and ones that are
> fully functional
> for around $1300.

I've seen a lot of U30's on EBay, some of them for as low as $750, but I
wont touch a one with less than 256megs of RAM, and at least one 4 gig
disk, in perfect condition, and from a seller with a good reputation. 

> On a personal note. I really like the head to head performace of
> UDMA100x7200RPMx2MB cache IDE HD's, against some very high end SCSI drives.
> In many cases, drive to drive shootouts between IDE and SCSI, IDE comes out
> on top for performance, and cost by a rather large margin. IDE has come a
> long way, and for small
> to medium performance desktops system that don't require RAID, IDE is the
> clear cut
> winner overall.
> 

In the cost per gigabyte race SCSI will always be beaten by UDMA just
based on the volume of parts shipped if nothing else.  on the
performance front there is a more complicated story.

When comparing single drive to single drive on the same system, a high
quality UDMA device will often best it's SCSI counterpart in
straightline benchmarks. These are indicitave of very good single device
single task performance. Change the configruation to two drives in each
system and the picture changes significantly in favor of SCSI. Four
drives skews the equation even more, because those four SCSI drives can
deliver their full sustained bandwidth all at the same time (each
typically higher than an equivalent IDE device), whereas the IDE devices
will each burst out their first 2 mb's, then each one will deliver maybe
10mb/s sustained througphut, and it doesnt add together because bus
mastering for IDE devices only works for one device at a time. 

My main need for SCSI is for multi tasking applications spread across
multiple devices. For example my primary PC has two IBM U160 hdd's, a
Plextor UltraSCSI 12x burner, and a Plextor UltraSCSI 32X CD-ROM all on
an adaptec card, and an external hp scsi scanner. This setup allows me
to Burn CD's while actually getting useful work done on my system. When
I was running that same system on primarily IDE devices burning a CD
completely occupied my system for 30 minutes at a time, and because of
the CPU load involved in scanning, or other image manipulation, starting
a job like that could tie up the system for long periods of time,
especially the IDE subsystem which is highly CPU dependant.

The primary purpose of my Sun systems (I currently have three, but I'm
getting rid of two of them) is as servers for my home network, as well
as my personal workstations for programming and security testing. It is
important to me to be able to use multiple devices simultaneously. 

For example I run backups from all of my systems (Windows, Mac, Sun,
Linux, and SGI) through my Sun U1-170 to an external tape drive every
night. At the same time I am often running compilations of system
utilities, or analyzing large logs. You can't do that sort of thing with
an IDE based storage subsystem. 

I also run video capture, image manipulation  (I'm also an aerospace
engineer, and my wife is a graphic artist and designer), modeling,
stress analysis, and other large transaction operations for which
multiple large transactions can be started simultaneously, something
that IDE isn't very good at (though it is very good at single large
transactions)

Finally I use one of my systems as a logger/sniffer/protocol analyzer
etc... for which there are huge numbers of extremely small transaction,
something which SCSI handles well, but IDE just kind of melts on.  

Also consider the advantage SCSI has in being a multipurpose bus. IDE is
limited to being an attachment only for disk drives, whereas SCSI can
and is used for a large variety of devices requiring high (or high
priority) bandwidth such as scanners, libraries, media production etc...

-- 
Chris Byrne
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The eyes may be the windows on the soul
But the word is the doorway to the mind
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