nixCraft

All -

We are attempting to restore from a SDLT tape drive off a Sun Server to a SDLT tape drive, Linux OS, 585 64 Bit server. We are currently getting the following errors and are at a loss on how to resolve, any thoughts?

[root@daa21267orc302 efiledump]# mt -f /dev/nst0 status

SCSI 2 tape drive:
File number=0, block number=0, partition=0.
Tape block size 0 bytes. Density code 0x49 (Quantum SDLT320). Soft error count since last status=0 General status bits on (41010000): BOT ONLINE IM_REP_EN

[root@daa21267orc302 efiledump]# tar xvf /dev/nst0
tar: /dev/nst0: Cannot read: Cannot allocate memory
tar: At beginning of tape, quitting now
tar: Error is not recoverable: exiting now

Use tar command as follows:
mt -f /dev/nst0 rewind
mt -f /dev/nst0 status
mt -f /dev/nst0 tell
tar --blocking-factor=128 -xvf /dev/nst0

--blocking-factor=N
Set N correct, this N is same used on solaris while you run the tar command. Default N=1 on solaris, howerver last time i done this it was value of 500 wored for me you can use mt -f /dev/nst0 status command to find the block size and use that as blocking-factor. This error only occurs if OS changes

Not sure about this error we use http://www.amanda.org/ Amanda backup software and it works without problem may be software does blocking-factor works.

A good doc to read @ http://www.ibiblio.org/pub/historic-...si/README.tape


dd and tar - blocking factor. How to determine the blocking factor, block size
so that tar and dd can work together.

Step 1: Create a large file on local disk, in a directory "1" that will eventually
be written to tape. This will be created with dd as follows:

$ mkdir 1
$ dd if=/dev/zero of=disk-image count=40960
40960+0 records in
40960+0 records out

$ cd ..

Step 2: tar the directory and contents to tape. First rewind the tape. These examples
use /dev/nst0 as the location of the tape. Make sure to substitute your values
if needed.

$ mt -f /dev/nst0 rewind
$ tar --label="Test 1" --create --blocking-factor=128 --file=/dev/nst0 1

Step 3: Read data from the tape using a block size of 128k. If you get an I/O error, which
could happend if you used a different blocking factor above, then, you may need
to increase the bs to 256, or 512 etc. as needed.

$ mt -f /dev/nst0 rewind
$ dd if=/dev/nst0 bs=128k of=testblocksz count=1
0+1 records in
0+1 records out

$ ls -l testblocksz
-rw-r--r-- 1 root root 65536 Feb 9 10:41 testblocksz

$ ls -lh testblocksz
-rw-r--r-- 1 root root 64k Feb 9 10:41 testblocksz

Note above that the size 65536 is equal to 64k. That "h" switch in "ls" is for
human readable.


Step 4: tar uses a multiplier of 512*blocking-factor to get block size. Again

512 * blocking-factor = block size used in dd command.

Putting in the values, we see that

512 * 128 = 65536


Step 5: So what does this tell you? You can now use these numbers to "dd" files
to tape. But, first tar will be used to create the file locally.

$ tar --label="Test 1" --create --blocking-factor=128 --file=test.tar 1


Step 6: Send this to tape with the dd command. Remember 64k is equal to 65536.

$ mt -f /dev/nst0 rewind
$ dd if=test.tar bs=64k of=/dev/nst0


Step 7: Now test that it can be read with tar command using blocking-factor=128.
Note the "t" command in tar is for tell. It will not write data.

$ mt -f /dev/nst0 rewind
$ tar -tvf /dev/nst0 --blocking-factor=128
V--------- 0/0 0 2005-02-09 10:38:20 Test 1--Volume Header--
drwxr-xr-x root/root 0 2005-02-09 10:34:10 1/
-rw-r--r-- root/root 20971520 2005-02-09 10:34:11 1/disk-image


Step 8: Reading tape data with dd. Most of the time a high "ibs" input block size

$ mt -f /dev/nst0 rewind
$ dd if=/dev/nst0 of=outfromdd.tar ibs=64k
321+0 records in
41088+0 records out


Step 9: Verify that outfromdd.tar can be read by tar with blocking-factor=128

$ tar -tvf outfromdd.tar --blocking-factor=128
V--------- 0/0 0 2005-02-09 10:38:20 Test 1--Volume Header--
drwxr-xr-x root/root 0 2005-02-09 10:34:10 1/
-rw-r--r-- root/root 20971520 2005-02-09 10:34:11 1/disk-image


PULLING FILES: The dd command can be used to pull files.

ssh target_address dd if=remotefile | dd of=localfile

Or, a specific example of getting a file from a computer called hamlet.

$ ssh root@hamlet dd if=/home/cvs/test | dd of=/home/storage/test


GOING BACKWARD AND FORWARD ON TAPE:

Go to end of data
$ mt -f /dev/nst0 eod

Previous record
$ mt -f /dev/nst0 bsfm 1

Forward record
$ mt -f /dev/nst0 fsf 1

Rewind
$ mt -f /dev/nst0 rewind

Tell
$ mt -f /dev/nst0 tell

(Reference TIP 151 - for how to get around firewall

Below is a script that I use to backup computers via ssh. The
tape drive is on "nis" and the extra space is on "hamlet".

#!/bin/bash
# Program to backup server remotely
# Assume remote server is nis, you are on squeezel
#
# Recover from tape
#
# dd if=/dev/nst0 of=test.tar.gz bs=64k
#
filename="support1.$(date "+%m%d%y%H%M").tar.gz"
DIRTOBACKUP=/var/www
#tar cvzf - $DIRTOBACKUP | ssh root@nis '(mt -f /dev/nst0 rewind; dd of=/dev/nst0 bs=64k )'
tar cvzf - $DIRTOBACKUP | ssh support1@hamlet "dd of=/home/support1/backups/${filename} "

Another example program, below, pushes the last ".tar.gz" file to tape:

#!/bin/bash
# Program to push files to tape
#
#
# Notes on recovering from tape
#
# dd if=/dev/nst0 of=test.tar.gz ibs=64k
# or
# $ ssh root@tapeserver "mt -f /dev/nst0 rewind"
# $ ssh root@tapeserver "dd if=/dev/nst0 ibs=64k"|dd of=cvs1.tar.gz
#
#
#
# First rewind tape
ssh root@tapeserver 'mt -f /dev/nst0 rewind'
#
# Grab only the last file
file=$(find /home/cvs -iname 'cvs*.tar.gz'|sort|tail -n 1)
dd if=${file}|ssh root@tapeserver 'dd of=/dev/nst0 bs=64k'

Source url: http://souptonuts.sourceforge.net/ho...pen_source.htm # 136 hope this helps you.