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Under UNIX, magnetic tape drives are given individual numbers, starting from zero. Tape drives are accessed by means of a device special file which is located in the /dev directory. These device special files appear to the user as normal files, which can be opened, read from and written to. All operations that you would do on a normal file can be done on a special file. The only difference is that the data in the file resides on the tape loaded in the drive, not on the filesystem. In addition, because there are different ways of physically writing data to a tape (e.g. low/high density), there are several different files that correspond to the same tape drive.
Each variant of UNIX has its own names for the tape drives. We will limit ourselves to linux
Tape devices under linux have different names depending on the type of
tape involved. The most common sort of tape (SCSI Tape) will have a device
name of 'st'.
So for example the first scsi tape will have the following device special files
/dev/st0 - normal rewinding scsi device /dev/nst0 - non-rewinding scsi tape device
Floppy tape drives (e.g. iomega ditto, Travan tapes and other QIC Format tape drives) will be called ;
/dev/rft0 - normal rewinding floppy tape device.
/dev/nrft0 - non-rewinding floppy tape device.
One major difference between Linux and Digital UNIX devices is that the density code is not used on linux. If you want to write a tape with a density other than the default (usually highest) density then you may need to use the mt command with the densities or setdensities arguments to set the density of the device. Read operations usually do not need the density setting explicitly, as this will be automatically picked up.
mt [-f tape_device] command [count]Where tape_device is one of the device special files discussed in the first section, normally a "no rewind" device like /dev/nrmt0h. The commands are detailed in the man page for "mt", but a few important ones will be listed here.
rewind Rewinds a tape. status Prints out information about a tape. offline Unloads a tape. fsf Forward Skip File. bsf Back Skip File. Some of these commands can take an argument, e.g.
mssly1~> mt -f /dev/nrmt0h fsf 2Will skip forward two files on a DAT on mssly1.
The drive name is optional, if you are accessing the first tape
drive (mt0). For all other drives the drive name must be explicitly
specified on the command line. This is good practice even if you are using
the default drive.
Rewind tape drive:
# mt -f /dev/st0 rewindBackup directory /www and /home with tar command (z - compressed):
# tar -czf /dev/st0 /www
Find out what block you are at with mt command:
mt -f /dev/st0 tell
Display list of files on tape drive:
# tar -tzf /dev/st0
Restore /www directory:
# cd /# mt -f /dev/st0 rewind
# tar -xzf /dev/st0 www
Unload the tape:
# mt -f /dev/st0 offline
Display status information about the tape unit:
# mt -f /dev/st0 status
Erase the tape:
# mt -f /dev/st0 erase
You can go BACKWARD or FORWARD on tape with mt command itself:
(a) Go to end of data:
# mt -f /dev/nst0 eod(b) Goto previous
# mt -f /dev/nst0 bsfm 1(c) Forward record:
-f /dev/nst0 fsf 1 Replace /dev/st0 with your actual tape drive name.
mt exits with a status of 0 if the operation succeeded, 1 if the operation or device name given was invalid, or 2 if the operation failed.
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