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Full Discussion: multi tape option in tar cmd
Operating Systems Linux Red Hat multi tape option in tar cmd Post 302566424 by Corona688 on Thursday 20th of October 2011 10:33:30 AM
Old 10-20-2011
If your version of tar can read from stdin, you can do something like this to avoid storing hundreds upon hundreds of gigabytes of temporary files:

Code:
# create tapes
mkfifo tarfifo
tar -vcf tarfifo /path/to/files &
PID=$!
N=0
while [ -d /proc/${PID} ]
do
        printf "Insert tape and hit enter " >&2
        read < /dev/tty # Read from terminal, not tarfifo
        dd of=/dev/tape bs=<tape_blocksize> count=<tape_blocks>
        eject_tape
        N=`expr $N + 1`
done <tarfifo

Code:
# extract tapes
mkfifo tarfifo
N=0
while [ -z "$INPUT" ]
do
        dd if=/dev/tape bs=<tape_blocksize> count=<tape_blocks>

        eject_tape

        # Print to stderr, so we don't feed this message into tar!
        printf "Insert tape and hit enter " >&2
        read INPUT
        N=`expr $N + 1`
done | tar -C /path/to/dest/ -xvf -

You could test this with local files instead of tapes by replacing /dev/tape with /path/to/file$N and using a small blocksize and blockcount.
Last edited by Corona688; 10-20-2011 at 11:40 AM..
This User Gave Thanks to Corona688 For This Post:
nithyanandan
 

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LEARN ABOUT NETBSD

mt

MT(1)							    BSD General Commands Manual 						     MT(1)

NAME

     mt -- magnetic tape manipulation

SYNOPSIS

     mt [-f tapename] command [count]

DESCRIPTION

     The mt program is used to give commands to a magnetic tape drive.	By default mt performs the requested operation once.  Operations may be
     performed multiple times by specifying count.

     Note that tapename must reference a raw (not block) tape device.  If tapename is of the form "host:tapename", or "user@host:tapename", mt
     writes to the named tape device on the remote host using rmt(8).

     The rmt(8) process on the remote host is typically initiated via rsh(1), although an alternate method such as ssh(1) can be specified via the
     RCMD_CMD environment variable.

     The available commands are listed below.  Only as many characters as are required to uniquely identify a command need be specified.

     asf	Move forward count files from the beginning of the tape.  This is accomplished by a rewind followed by fsf count.

     eof, weof	Write count end-of-file marks at the current position on the tape.

     fsf	Forward space count files.

     fsr	Forward space count records.

     bsf	Back space count files.

     bsr	Back space count records.

     rewind	Rewind the tape.  (The count is ignored.)

     offline, rewoffl
		Rewind the tape and place the tape unit off-line.  Where supported, this ejects the tape.  (The count is ignored.)

     status	Print status information about the tape unit.  (The count is ignored.)

     retension	Retensions the tape.  Not all tape drives support this feature.  (The count is ignored.)

     erase	Erases the tape Not all tape drives support this feature.  (The count is ignored.)

     eew	Enable or disable early warning EOM behaviour.	Set count to nonzero to enable, zero to disable.

     eom	Forward space to the end of recorded media.  (The count is ignored.)

     blocksize, setblk
		Set the tape blocksize to count bytes.	A count of zero sets variable blocksize.

     density, setdensity
		Set the tape density code to count as specified in the SCSI-3 specification.  See the DENSITY CODES section for a list of codes
		for commonly used media types.

     rdspos	Read the logical block position of the tape.  Not all tape drives support this feature.  (The count is ignored.)

     rdhpos	Read the hardware block position of the tape.  Not all tape drives support this feature.  (The count is ignored.)

     setspos	Set the logical block position of the tape to count.  Not all tape drives support this feature.

     sethpos	Set the hardware block position of the tape to count.  Not all tape drives support this feature.

     compress	If count is zero, disable compression.	Otherwise enable compression.  Not all tape drives support this feature.

     If a tape name is not specified, and the environment variable TAPE is not set, then mt uses the device /dev/nrst0.

ENVIRONMENT

     If the following environment variables exist, they are used by mt.

     TAPE	 mt uses device filename given in the TAPE environment variable if the tapename argument is not given.

     RCMD_CMD	 mt will use RCMD_CMD rather than /usr/bin/rsh to invoke rmt(8) on a remote machine.  The full path name must be specified.

FILES

     /dev/rst*	Raw SCSI tape device
     /dev/rmt*	Raw magnetic tape device

EXIT STATUS

     mt returns a 0 exit status when the operation(s) were successful, 1 if the command was unrecognized, and 2 if an operation failed.

DENSITY CODES

     The SCSI-3 specification defines a number of density codes for various tape media, some of which are listed here.	Note that many tape drive
     vendors also define model-specific codes.

     Code    Format
     0	     Device default
     1	     1/2" 800 bpi
     2	     1/2" 1600 bpi
     3	     1/2" 6250 bpi
     4	     QIC-11
     5	     QIC-24
     15      QIC-120
     16      QIC-150
     17      QIC-320/525
     18      QIC-1320/1350
     19      DDS
     28      QIC-385M
     29      QIC-410M
     30      QIC-1000C
     31      QIC-2100C
     32      QIC-6GB
     33      QIC-20GB
     34      QIC-2GB
     35      QIC-875M
     36      DDS-2
     37      DDS-3
     38      DDS-4

SEE ALSO

     dd(1), ioctl(2), mtio(4), st(4), environ(7)

HISTORY

     The mt utility appeared in 4.3BSD.

BSD
								   March 9, 2008							       BSD
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