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Old 05-02-2005, 05:50 PM   #1
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Using dd to get an image of a DLT tape

Anybody have any suggestions using dd to extract an image copy off of a DLT VS160 tape? The problem is that a large backup was overwritten with 4 megs of data. By normal means, the previous backup is gone. The tape drive is properly configured in SUSE 9.2 - details below. The 4 meg backup is 4065280 bytes in size. I have to use a block size of 65536 or larger (bs=64k) otherwise get "cannot allocate memory" error. So far I can only get the backup header off the tape. Some examples I've used so far are:
dd if=/dev/st0 of=/media/tape.dd bs=64k
dd if=/dev/st0 of=/media/tape.dd bs=1024k
dd ibs=1024k conv=noerror,block if=/dev/st0 of=/media/tape.dd
dd if=/dev/st0 bs=4065280 skip=1 | dd bs=1024k | dd of=/media/tape.dd seek=1

and various others using different block sizes etc.

Tape drive info:
st: Version 20040403, fixed bufsize 32768, s/g segs 256
(scsi2:A:5): 160.000MB/s transfers (80.000MHz DT, offset 96, 16bit)
Vendor: QUANTUM Model: DLT VS160 Rev: 2500
Type: Sequential-Access ANSI SCSI revision: 02
Attached scsi tape st0 at scsi2, channel 0, id 5, lun 0
st0: try direct i/o: yes (alignment 512 B), max page reachable by HBA 1048575
Attached scsi generic sg0 at scsi2, channel 0, id 5, lun 0, type 1

mt -f /dev/st0 status
drive type = Generic SCSI-2 tape
drive status = 1342177280
sense key error = 0
residue count = 0
file number = 0
block number = 0
Tape block size 0 bytes. Density code 0x50 (unknown).
Soft error count since last status=0
General status bits on (45010000):

Any suggestions would be great!
Old 05-02-2005, 07:28 PM   #2
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Have you tried:
dd if=/dev/st0 of=/media/tape.dd bs=64k count=64
Old 05-02-2005, 07:46 PM   #3
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Thanks, I just did and got the same results. I'm begining to think it's just a limitation of dd; it reaches the eof mark on the first record, which is the job header of the backup tape and quits. That's why I can't get past the first filemark. There's gotta be a way to get that data that's lying beyond the 4 meg worth of overwritten info.

Thanks for replying,


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