Why Buy I-P-I? SCSI is equally fast and 40% cheaper

[ekrell at ulysses.att.com]

You can't just look at the transfer rate and seek time to compare 2
different disk subsystems. The controller makes a big difference. Example:
we have a Sun 4/490 and a Solbourne Series 5/802.  Both machines have the
Imprimis Sabre 1.2GB disks. Sun uses the disk with the IPI interface and
Solbourne uses the SMD interface. Other than that, the two disks are
identical (both have a 3MB/s transfer rate).

The Sun has 2 of these disks on the Sun IPI controller. The Solbourne has
2 of the SMD disks on the Xylogics 753 controller. Both systems have the
same SPARC CPU and 32MB of memory and are running basically the same
operating system (SunOS 4.0.3).

Running disk I/O benchmarks reveals that the IPI controller is about 25%
faster than the XY753 in writing data to the disk (reading times were
comparable). This is probably due to the 1MB cache on the Sun IPI
controller, but the point is that 2 different controllers with essentially
the same disk can perform quite differently.

Eduardo Krell                   AT&T Bell Laboratories, Murray Hill, NJ

UUCP: {att,decvax,ucbvax}!ulysses!ekrell  Internet: ekrell at ulysses.att.com