Help upgrading disks

[dfutche at relay.nswc.navy.mil]

We are in the process of trying to upgrade our on-line disk capacity and
are becoming frustrated with the conflicting information we have received
from the various suppliers of Sun-compatable disks and controllers.  We
would appreciate any advice or enlightenmentthat  anyone would like to
offer.  

We are currently configured with a 4/370 serving a combination of 8 4/65
and 3/60 diskless work stations.  The server has 3 disks consisting of 2
Fujitsu Eagles  controlled by a single Xylogics 450/451 and an 892
megabyte Hitachi controlled by a Zylogics 7053 (smd-4).  Our original plan
was to add an IPI controller and 2 gigabytes of disk storage.  We have
found at least one vender who says they can provide this solution at what
we believe is a reasonable cost.   However acording to our Sun
representatives, the IPI controller is not supported on the 4/370.  Is
this true?  Does anyone have any experience with an IPI and the 4/370
configuration.  Info on reliability and the availability of maintenance
would be especially appreciated.   

In addition to the controller question, we have received mixed signals
concerning the disk capacity issues.  Do the large disks (2 gigabyte
range) have real performance and reliability problems?  We will probably
want to get rid of the 2 small Fujitsu disks in order to accomplish the
upgrade and therefore less than 2 gigabytes of new storage  would not be
worth the effort or expense.  Sun's proposals so far  would involve
purchasing 2 or 3 disks to achieve this goal.  As their disk prices seem
to be considerably higher than those quoted by the third party vendors, we
would like to know if the trade-offs are justified.  Our priority in this
purchase is increased disk storage, but we would of course like to get as
much performance as we can aford.  Again, we would appreciate any
information you might have on ipi and 4/370 compatability as well as any
other disk expansion options you can point out.  Thanks in advance.

Debbie Futcher  (dfutche at relay.nswc.navy.mil)