DEC Data Retrieval - test-drb@ccmp.vtda.org

29 Jan 2014

On 2014-01-29 10:00, Paul Koning<paulkoning at comcast.net> wrote:
...

 On Jan 29, 2014, at 1:39 AM, Johnny Billquist<bqt at Update.UU.SE>  wrote:

  >Right. Different PDP-11 OSes use different
formats, so it's not really meaningful to ask about "PDP-11 backup". You
need to specify which backup format you are talking about.
 >I think I know of at least four.
 >
 >RSX used to use something called DSC (which stood for Disc Save and Compress), which
was eventually replaced by BRU.  There was an irreverent reading for DSC: ?disk
smash and corrupt?. 
Ayup. I usually pretend I've never heard of DSC. :-)

...
  I forgot what IAS (and RSX11-D) used.  DSC possibly.

Yes. As far as I can remember. I'm also pretty sure IAS got BRU by the end.

...
   >I assume
RSTS/E had some backup format in the older days. With RSTS/E V9 (I think it was), a new
backup utility was created, which is the VMS compatible one.  V9 sounds right.  It
was coincident with support for streaming tape drives, which needed asynchronous (queued)
I/O to work properly, and that in turn meant serious work on the backup program.  The
designer decided to adopt the VMS backup format as a good one to use (because of things
like XOR block redundancy and CRC data integrity checks). 
Makes sense, and it's a nice idea to use the same format. In a way, it 
would have been nice if RSX had done the same. BRU, while good in many 
ways, is a hairy piece of code. It could have used another rewrite...

...
  Before then there was a crude program also called
Backup (but entirely unrelated) that could do partial backups.  And an entirely different
program called SAVRES (save/restore) that would do whole disk backup but could, I think,
do partial restores.  And going back even further, there was ROLLIN ? that?s just a full
disk image copy, to another identical disk, or DECtape(s) (or perhaps also magtape, I
don?t remember).  None of those older programs were compatible with any other OS. 
SAVRES and ROLLIN rings bells, now that you mention them. Thanks. :-)

...
   >I'm
not aware if RT-11 also had some backup tool, but I would assume so.  There?s always
PIP, of course. 
Of course. But that implies some structure on the tape that (at least 
under RSX) is outside the control of PIP.
But yes, DOS-11 is the plain format for files on tapes used by RT-11, as 
far as I know.

	Johnny