User`s guide

BACKUP
The following command backs up all files on DU0 of type OBJ to a logical
disk, OBJ.DSK on device DU1. The success of the operation is verified by
including the /VERIFY option in the command:
.BACKUP/VERIFY DU0:*.OBJ/SUBSET DU1:OBJ
The command displays all files backed up to DU1. If DU1 does not contain
sufficient free blocks for all the OBJ files, BUP returns an error message
indicating insufficient space, and no files are backed up.
Advantages of Using BACKUP to Back Up Logical Disks
The advantages of using the BACKUP command to back up information into
logical disks are the following:
• You perform no CREATE, INITIALIZE, or MOUNT operations; the
/SUBSET option performs the equivalent of those operations for you.
• The logical disk created by the /SUBSET option is identical to one you
create manually, except no free blocks are allocated and the number of
directory segments is only sufficient to contain the files being backed up.
This makes for efficient storage of the information in logical disks and for
ease in accessing it, since it remains a logical disk.
Disadvantages of Using BACKUP to Back Up Logical Disks
The disadvantages of using the BACKUP command to back up information
into logical disks are the following:
• The /SUBSET option is an alternative to the /SAVESET option, but, unlike
savesets, logical-disk images created by the /SUBSET option must reside
on a single backup volume.
• The /SUBSET option is appropriate only for file operations. You cannot
back up entire volumes (disk images) to logical disks with this option.
You can use the COPY/DEVICE command for that type of operation. This
means that, although BACKUP with the /SUBSET option will move all
the files on a disk to a logical disk, that command will not copy the boot
blocks.
2. Listing directories of logical disks
To get a directory of a logical disk, specify the [ldname]/SUBSET option with
the BACKUP/DIRECTORY option.
24 RT–11 Command Descriptions