RA81's hanging??

[Chris Torek]

RA81s don't ``always hang''; however, there are lots of problems with them:

	a) nobody seems to have a decent driver for UDA50s;
	b) early UDA50s had microcode bugs that kept taking drives
	   off line;
	c) UDA50s take up too much Unibus +5 power;
	d) they're *slow* (at least for Unix; dunno about VMS);
	e) ??? who knows.

They do have the advantage that you can plug in lots of disk space to
one controller, and they don't need massbi (plural of massbus); i.e.,
they're relatively cheap.  (And 450 Mbytes per disk is kinda nice.)

We have two 750s with only RA81s and one 780 (in EE) with two RA81s and
two RK07s.  The RK07s are as bad as the RA81s for hardware problems
(packs go bad all the time and so forth).

I said before (and now repeat) that the ``df hangs'' bug with RA81s is
due to a bug in udopen(), where a command is started then a sleep is
done, but without blocking interrupts in between.  More serious (to me
at least) was the ``SHOULD REQUEUE OUTSTANDING I/O REQUESTS'' comment
in the UDA hard error code; we were having lots of system crashes due
to that, it seemed, so I wrote the requeue code and it seemed to help.
But we still have software problems with the driver.
-- 
(This mind accidently left blank.)

In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (301) 454-7690
UUCP:	{seismo,allegra,brl-bmd}!umcp-cs!chris
CSNet:	chris at umcp-cs		ARPA:	chris at maryland