Emulex MD21 vs. Adaptec ACB4000

[Anthony A. Datri]

I see that there are different sets of supported disks under these two
controller types in Sun's 4.0 format.dat file.  The Micropolis 1355 is
listed under the MD21, yet I have a Sun sheobox with a 1355 attached to an
Adaptec.  Is this division as arbitrary as it seems?  I want to take a DEC
rd53 (really a Micropolis 1325), and hang it as the second drive off of
the MD21 in a Sun shoebox that already has a 1355 in it.  I suspect that
this'll work just fine as long as I add an entry for the 1325 off of the
MD21.

I can see that the smaller ribbon from the drive goes directly to the
empty set of pins on the MD21, but do I have to substitute a ribbon with
two connectors for the larger, with both drives chained?  Does adding a
second drive to the MD21 affect performance adversely?  In a previous
incarnation, we attached a Maxtor 1140 to an Adaptec/1325 equipped
shoebox, and it seemed to work fine after we figured out the geometry.