On Fri, 10 May 1996 14:51:37 EDT Stan Horwitz <[log in to unmask]> said:
 
>I was just told by one of the people who runs the system on which we run
>Listserv that if we  were to shut Listserv down to back  it up, it would
>be down for several hours
 
Uh? What is your backup device, a 3410-1 with a tape mount in between and
the operator watching a  movie that's so good he can't  get away from the
TV until  it's over?  :-) LISTSERV  191 is typically  20-30 cyl  at large
sites, it should only take a couple minutes to back up. Alternatively you
could create a shadow 191 minidisk  and have LISTSERV copy the files over
once a day, then release and detach the disk. You could then back up this
alternate minidisk instead of the 191.
 
In general  the problem of  making reliable backups  on a live  system is
unsolved. The system that comes closest  is OSF/1, the backup program can
tell the  system to take  a snapshot of an  entire partition so  that the
backup  program sees  the  files as  of this  instant  regardless of  any
further change (a bit like SFS, but  for the entire file system). But not
even that ensures that the snapshot  is in a stable state. An application
could be in the process of appending to a file, etc. Any application that
can  recover  automatically  from  a power  outage  should  recover  from
restoration  of  such a  backup,  but  ordinary  end users  seldom  write
applications this way :-) As far as I know, OSF/1 is the only system that
can do  that. I  hope and assume  that TNFS will  also have  this ability
under VMS.
 
  Eric