On 2018-01-25 22:57, Mark Pizzolato wrote:
I think the documentation comment “cannot write variable-length blocks
and do not allow skipping forward over records between read operations”
was written when talking about the common cartridge tapes that were
available on 80s and 90s Unix workstations. I don’t recall the name.
These things only supported fixed block size operations and not variable
record lengths (i.e. 80 byte tape labels, then different sized data
records, etc.).
Exabytes?
I know there was some people who thought they couldn't do variable size
reocrds, but that is actually incorrect. They can. It might be wasting
space on the underlying tape or something, I don't know. But I certainly
had Exabytes connected to VAXen and PDP-11s, and used the normal DEC
tools to play around, and Exabytes behaves just like any other tape
drive, in all aspects.
Johnny
Given that the remote tape drive was a drive which
could do variable length record activities, I think MultiNet’s rmt
support actually worked well. I don’t remember testing it though.
Whether someone should try to do that now to backup simulated VMS
systems is another subject I may write about a little later.
*From:*Simh [mailto:simh-boun...@trailing-edge.com] *On Behalf Of *Clem Cole
*Sent:* Thursday, January 25, 2018 1:31 PM
*To:* Larry Baker <ba...@usgs.gov>; SIMH <simh@trailing-edge.com>
*Subject:* Re: [Simh] VAX Tape Emulation?
On Thu, Jan 25, 2018 at 4:14 PM, Larry Baker <ba...@usgs.gov
<mailto:ba...@usgs.gov>> wrote:
Because UNIX tapes and tape driverscannot write variable-length
blocks and do not allow skipping forward over records between read
operations
That's not a correct statement. UNIX does it great - I've used it
(and rmt) for years. UNIX's tape driver is the most flexible of any OS
I have ever used (and I have done tapes on probably greater than 25
different OS's over the last 40 years). That's why I suggest it. I
wonder what the issue for VMS is?
Hmm.. thinking about it, TCP sockets will remove the record orientation
(TCP creates an stream of octets without any records), so if you are
doing the funky RMS like stuff, its TCP that dropping those boundaries
not the UNIX tape driver. If you want same then it need to be set as
meta-data. But the UNIX tape drive works as expected. The 'block'
size is the size of the write, although I think the TM11 requires a
minimum of 512 bytes. Records passed with the MTIO ioctl' which mt/rmt
all support..
That said, I agree if he can get DECnet to work, that is likely to
better integrated into the utilities.
Clem
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