🚀 go-pugleaf

I wrote:
> 
> I just hooked up an Archive Python DAT drive to a mono NeXTstation.  I
> find that I cannot dump the internal hard drive to the tape.  I've
> dumped both (large) partitions of an external drive with no trouble,
> and tried different tapes.  Dump complains about a "tape write error"
> after writing a fraction of the tape and the following ends up on the
> console:
> 
> 
> sd1 (1,0): scsi_timer: timeout op:0x28 sd_state:7 scsi status:0x0
> Target 6: BUSY; retry 1
> ..
> ..[etc]
> ..
> Target 6: BUSY; retry 16
> st: cmd = 0xa sr_io_status = 2H
>     Sense key = 0x6  Sense Code = 0x29

The problem seems to have been with a too long SCSI cable.  I had (for
historical reasons) 6+6+2=14 feet of cable hooking three devices to
the NeXT.  The SCSI standard calls for a 6 m (= 19.7ft) maximum cable
length.  Replacing one of the 6ft cables with a 1.5 foot cable made
dump very reliable where it had failed consistently before the switch.

I'm somewhat concerned that I got into cable length trouble with 5.7ft
less cable than the maximum.  I read in a manual for a DECstation 5000
that each device on the bus (including the CPU) counts for some amount
of cable length due to internal cabling.  Perhaps this is the source
of the extra length? 


Christopher B. Moore
cmoore@maggie.mit.edu
MIT Astrophysics