3rd Party SCI Disks

[Alan's Home for Wayward Notes File.]

In article <15166 at dartvax.Dartmouth.EDU>, steve at avalon.dartmouth.edu (Steve Campbell) writes:
> We are considering purchasing a larger DEC RISC processor (5810), and
> are thinking of buying 3rd party disks.  Emulex offers a disk stack
> containing their SD891 drives, which are CDC drives with an Emulex
> module attached.  Emulex claims that the result is an MSCP/SDI-
> compatible unit that can be controlled by the KDB50 just like a DEC
> drive such as an RA90.  Would anyone care to comment on whether this
> will work under Ultrix 3.X?  If not, why not?

	It may work as a data disk.  It may not work as a system
	disk.  Why?  Ultrix only supports DEC drives.  If 3rd
	party drives work, fine; if not, take it up with the 3rd
	party.  Previous experience with V3.0 and the VAX has
	shown that VMB doesn't get along with 3rd party emulations
	of MSCP disks.  The boot path on the 58xx may not be as
	limited, but there is some advantage of putting the system
	disk on a supported disk.
> 
> We have also heard that although the KDB50 can nominally run up to 4
> disk drives, there is a performance penalty if more than 2 are connected.
> Again, can anyone comment?  Any specific figures on the penalty?
> 

	Doing a simple sequential read of a large file on an RA90
	connected to a KDB50 on my VAX 8800 I can get around 800
	KB per second (one disk).  When I add a 2nd disk the per
	disk goes to around 450, and the total to around 900.  For
	three disks the total averages in the upper 900's.  With
	all four disks going it's about 1000 KB/sec.  In each case
	the "per drive" bandwidth was in proportion to the number
	of drives.  

	The performance you see will depend on the application.  If
	there isn't much seeking going on you're doing sequential
	reads of large files then the numbers I gave may be useful.
	There were the results of an exceptionally simple minded
	experiment that I ran while composing this follow.  They
	should be taken as an official performance study given by
	DIGITAL.  Your mileage may vary depending on the configuation
	and application.
-- 
Alan Rollow				alan%nabeth.dec.com at decwrl.dec.com