[comp.os.vms] Emulex TC13 tape controller

cetron%ced@CS.UTAH.EDU (Ed Cetron) (11/07/87)

the first big question to address is where is the 'source' of the backup and
the second which device are you getting the data lates from.  If you are
backing up over the ethernet from a satellite to the tape, and the tape is
before the delua (which is not highly buffered) you will likely see some
real problems.  We say similar problems on a PDP-11 unibus and found that the
best arrangement turned out to be putting the tape AFTER the uda-50 AND slowing
down the uda-50 by setting the appropriate jumper - bizarre but it worked.

-ed
cetron@cs.utah.edu

dunnett@mala.bcc.CDN (Malcolm Dunnett) (11/08/87)

I have a VAX 780 with the following Unibus Configuration

   DW780 -->  DELUA
              Emulex TC13  ( controlling Fujitsu M2444AC tape drive )
              LP11
              Able VMZ32 (3)
              DUP-11
              DZ-11E
              UDA-50

The system is the boot member of a LAVC which has 2 MicroVax II satellite
nodes.

The problem I'm having is that when I do a BACKUP to the tape drive I get
about 40 to 50 "Data Late" errors. These seem to be recoverable and do not
affect the integrity of the save set, but they are annoying.

I assume that the problem comes from the DELUA ( which is closer to the CPU )
"hogging the bus". If this is the case then it seems that swapping the order
of the DELUA and the TC13 might fix the problem. Does this sound reasonable?
Is it likely to cause any problems for the DELUA if it's not first ( DEC
recommends that for "optimum performance" it be first, but they don't specify
how much less than "optimum" is still going to work )

I'd appreciate hearing from anyone who has had experience with a similar
configuration or particularly has solved this problem.

Thanks in advance


Malcolm Dunnett
Malaspina College
Nanaimo, BC Canada

(604)753-3245