Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!fed!m1rcd00
From: m1rcd00@fed.frb.gov (Bob Drzyzgula)
Newsgroups: comp.periphs
Subject: Disk Performance
Keywords: SCSI IPI
Message-ID: <934@arccs2.fed.FRB.GOV>
Date: 1 Feb 91 18:20:27 GMT
Sender: news@fed.FRB.GOV
Reply-To: rcd@fed.frb.gov (Bob Drzyzgula)
Organization: Federal Reserve Board, Wash, DC
Lines: 59

I am thinking about the purchase of a large SPARC server that would be
used by a couple dozen people. One thing I need to consider is what
kinds of disk drives to use. It is important that the disks that are
chosen offer the best possible performance, without going to outragous
cost.

In the past couple of years, drive interface technology has, as we all
know, been changing quite substantially. Among other things, the result
of all this change is some confusion, or at least lack of
understanding, on my part.  I'd like to correct this, if possible.

A recent product line overview from Seagate illustrates my question fairly
well. Look at the following table:

                  Interface  Nom. Cap. (MB)  xfer rate (MBps)    avg seek (ms)

8" Sabre-6 8HP      IPI-2        2105            24.0              12
8" Sabre-7          IPI-2        3220             4.67             12
8" Sabre-7 2HP      IPI-2        3050             9.34             12

5.25" Elite-1       IPI-2        1200             3.0              11.5  
5.25" Elite-1       SCSI-2       1600             5.0              11.5


Now, without taking into consideration the physical size of the drive,
or the cost, it seems that one would build a machine with the Sabre-6
8HPs. But if you do think about cost, you might discover that you can
get maybe four of the Elite-1s for about the same price. If you then
decide that the lower cost of the Elites justifies sacrificing the high
transfer rates, then how does one decide on an interface?  I'd like to
know that the comparison between SCSI-2 and IPI-2 isn't (or is) as that
between apples and oranges. Is there any reason to prefer a 3.0 MB/Sec
IPI over a 5.0 MB/Sec SCSI? Is there any difference between the
performance characteristics of the two interfaces that would make one
decide that one humungus 4.67 MB/Sec IPI drive is better than two
half-humungus 5.0 MB/Sec SCSI drives, even if the cost is a little
higher? What about the 9.34 MB/Sec drive? What is the state of IPI
controllers and SCSI host adaptors to handle these speeds, and how do
they hold up with multiple devices attached? How do characteristics of
the workload affect these arguments?

Does anyone know if there is any chance that we will soon be able to
carve up these enormous drives into more than 8 partitions on under
SunOS?

These and other questions about drive and controller performance haunt
me as I think about how to spend this fairly large chunk of money. Can
anyone point me in the direction of research papers, white papers,
corporate glossies, etc. etc. that would help me to make these decisions?
Does anyone have thoughts of their own that they would like to share
with me?

Please email responses and I will summarize for the net, if there is
interest...

Thanks,
Bob Drzyzgula
Federal Reserve Board
rcd@fed.frb.gov