[lug] RH Linux download + hdparm

[D. Stimits]

John Karns wrote:
> 
> On Wed, 24 Oct 2001, D. Stimits said:
> 
> > John Karns wrote:
> > >
> > > On Tue, 23 Oct 2001, D. Stimits said:
> > > I'm mystified.  The drive is a 68-pin Quantum Atlas V with active
> > > termination, rated at 29MB/s, 7200rpm.  Must be the controller or mobo.
> > > The machine is not process bound either (virtually idle), so I doubt that
> > > the bus is i/o bound.  Although it could be a mobo design issue I suppose
> > > - it's showing its age.  It would be interesting to read some performance
> > > specs on those mobos.
> 
> Oops, the drive doesn't have active termination.  Rather, I
> have an active terminator connected to the bus cable.

The failure to use proper termination will cut burst speed down, I
*think* probably to 40 MB/s. From what you just said, I don't know if it
is correct or not in your case.

> 
> > What is the total capacity? I don't think there is such a thing as a
> > 7200 rpm drive that can average 29 MB/s. They lied. Unless maybe it is
> > one of those 180 GB drives. You'll get 31 MB/s with a 10k rpm 36 GB
> > drive with reasonably dense clusters. Are you sure there is no fine
> > print with some stipulation like "29 MB/s on outer tracks only, and
> > unfragmented systems"? Sorry, I'm skeptical of any 7200 rpm drive that
> > claims over 20 MB/s.
> 
> Capacity is 9.1 GB.  Specs from the Quantum site:
> 
> Exceptional value - 36.7GB, 18.3GB, and 9.1GB in a 1-inch-high, 3.5-inch
> form factor.
> 
> Outstanding performance - 7,200 RPM, 6.3 ms average seek time, 29MB/sec
> maximum sustained throughput, up to 160MB/sec bus transfer rate.

My 10k rpm, 36 GB (relatively high density) drive has a 31 MB/s
continuous throughput. The drive they refer to with 29 MB/sec is the
36.7 GB drive at 10k rpm. The best you'll get based just on rpm:
(7200/10000) * 31 = 22.3 MB/s

Very likely cluster density is about 10% or more lower on a 9.1 GB
drive:
22.3 * .9 = 20

Burst rate with full termination and u160 is up to 160 MB/s, usually
closer to 140 MB/s. The larger the cache in the drive, the more useful
that burst is. The 6.3 ms seek time is useful in being able to maintain
closer to the continuous throughput under random access (as opposed to
contiguous access), and more cache ram works in combination with fast
access...but it won't otherwise help average throughput.

> 
> > You never need to worry about dma settings or cpu useage on scsi. Not in
> > all cases, but in many, it plays nicer with the system as well. As soon
> > as you add multiple devices to it, advantages show up real fast in
> > comparison to IDE.
> 
> Another advantage is in having external devices, such as Zip and Jaz
> drives, Tape, and scanner.  These can be used in various combinations and
> connect easily to portables too.  Although in many cases one can get by
> with the parallel port versions, they're a lot slower and in more
> difficult to deal with both in terms of drivers and using multiple
> devices.

Multiple peripherals via scsi is just very convenient.

D. Stimits, stimits at idcomm.com

> 
> ----------------------------------------------------------------
> John Karns                                        jkarns at csd.net
> 
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