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

[F. L. Charles Seeger III]

In article <6551 at brazos.Rice.edu> gnu at toad.com writes:
|X-Sun-Spots-Digest: Volume 9, Issue 117, message 8
|[For 1.2 GB, 3Mbyte/sec or 6Mbyte/sec transfer rates, 16-18ms average access]
|
|I have found two synchronous SCSI drives in the same performance range,
|with much lower prices.

 [and mentions "up to 4MB/sec synchronous SCSI transfer rate"]

Though modern SCSI drives are quite cost effective, the 4 MB/s transfer
rate is misleading because this represents a drive cache to SCSI bus
transfer.  The raw rate from the media to the cache varies with drives,
but figures in the range of 2.5-3.0 MB/s are the best that I have seen.
That is a long way from the IPI 6 MB/s mark (which is achieved by reading
from two heads in parallel).

However, these drives don't make sense everywhere.  If the workload is
mostly disk service over an Ethernet, then the 6 MB/s can't be fully
utilized.  And they are rather expensive.  But, if you have a multi-user
machine, FDDI nets, or disk intensive applications to run locally, then
the 2+ speed advantage may be just the ticket.

So, I take strong exception to the statement in the subject line that SCSI
disks are as fast as the IPI disks.  They aren't.  Even using a pair of
SCSI disks in parallel on separate controllers may not be nearly as fast.
It all depends on the application.  However, I do agree that in most
historic Sun applications, the SCSI drives are a better choice.  Afterall,
the people at Auspex are pretty bright, and that is their choice.  Getting
the most reliable drives available is another lesson that we can all learn
from them.  Seek times and tranfer rates aren't everything.

And Sun is not yet delivering the 6 MB/s drives....  But, most of us have
IPI and FDDI in our future.  Just a matter of time.

  Charles Seeger    E301 CSE Building        Work: +1 904 392 1508
  CIS Department    University of Florida    FAX:  +1 904 392 1220
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