backup Post: 302287634

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Operating Systems AIX backup Post 302287634 by bakunin on Saturday 14th of February 2009 07:02:14 PM

02-14-2009

Registered User

Quote:

Originally Posted by zaxxon

I am too lazy to walk to the server room to test it with a tape, but when you write 1 file to tape with tar, and after that another, I guess you just overwrite the 1st or if they are both on the tape, you have to spool around.

This is true, but only in principle. The complete picture is quite more complex because of the somewhat counterintuitive way AIX is dealing with tape-drives:

You sure know that to access the tape you use a device like /dev/rmt0, yes? This is the tape drive in its standard configuration, the attributes shown if you do a "lscfg -vp rmt0" or a "lsattr -El rmt0" respectively.

But you might also have seen device specifications like "/dev/rmt0.1" or such. Have you ever wondered what they stand for? Well, i have not found a complete table up until now, but the principle is: it is the same tapedrive minus selected properties and every sub-number (/dev/rmt0.1, /dev/rmt0.2, etc..) stands for some capability or several capabilities which are "switched off" from the original drive.

Why does that have to do with the posters problem you ask: the standard drives (/dev/rmt0) of all IBM drives i know have an auto-rewind-feature. As soon as the tar output is written to the tape it is rewound back to its beginning. /dev/rmt0.1 (as the poster has found out to use) is the same drive but with this auto-rewind feature switched off.

Btw., there is also another way to navigate your way through a multi-session tape with several entries, like, for instance, an mksysb-tape: use the "tctl" command with the "fsf" subfunction. "fsf" is for "forward skip file" and is followed by a number indicating how many files to skip. For instance to write a file after an already written on use the following:

Code:

( tctl fsf 1 ; tar -cvf /dev/rmt0 /path/to/file )

Or, to read the backup of the filesystems in a mksysb tape, which is the fourth file on the tape:

Code:

tctl fsf 3 ; tar -tvf /dev/rmt0

I hope this helps.

bakunin

bakunin

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LEARN ABOUT REDHAT

ammt

AMMT(8) 						      System Manager's Manual							   AMMT(8)

NAME

       ammt - Amanda version of mt

SYNOPSIS

       ammt [ -d ] [ -f|-t device ] command [ count ]

DESCRIPTION

       Ammt  provides just enough of the standard mt command for the needs of Amanda.  This is handy when doing a full restore and the standard mt
       program has not yet been found.

       Ammt also provides access to the Amanda output drivers that support various tape simulations.

       See the amanda(8) man page for more details about Amanda.  See the OUTPUT DRIVERS section of amanda(8) for more information on  the  Amanda
       output drivers.

OPTIONS

       -d     Turn on debugging output.

       -f device
	      Access tape device device.  If not specified, the TAPE environment variable is used.

       -t device
	      Same as -f.

       command count
	      Which command to issue, and an optional count of operations.

COMMANDS

       Each command may be abbreviated to whatever length makes it unique.

       eof|weof count
	      Write count (default: 1) end of file marks (tapemarks).

       fsf count
	      Skip forward count (default: 1) files.

       bsf count
	      Skip backward count (default: 1) files.

       asf count
	      Position to file number count (default: 0) where zero is beginning of tape.  This is the same as a rewind followed by a fsf count.

       rewind Rewind to beginning of tape.

       offline|rewoffl
	      Rewind to beginning of tape and unload the tape from the drive.

       status Report  status information about the drive.  Which data reported, and what it means, depends on the underlying operating system, and
	      may include:

	      ONLINE Indicates the drive is online and ready.

	      OFFLINE
		     Indicates the drive is offline or not ready.

	      BOT    Indicates the drive is at beginning of tape.

	      EOT    Indicates the drive is at end of tape.

	      PROTECTED
		     Indicates the tape is write protected.

	      ds     Device status.

	      er     Error register.

	      fileno Current tape file number.

	      blkno  Current tape block number file.

	      NOTE: many systems only report good data when a tape is in the drive and ready.

AUTHOR

       Marc Mengel <mengel@fnal.gov>
       John R. Jackson <jrj@purdue.edu>

SEE ALSO

       amanda(8)

																	   AMMT(8)