Cannot backup over 12GB on HP C1537A DDS-3 Tape Drive

[Alvin K. T. Ko]

I've a C1537A DDS-3 Tape Drive in my Linux. I use 'dump 0uaf /dev/nst0 /export/hom' to backup my /export/home folder which has 23198MB data. I need to change another backup tape when about 45% completed.

I've checked with 'mt -f /dev/nst0 status' and find the hardware compression has been turned on.
### mt -f /dev/nst0 status ###
SCSI 2 tape drive:
File number=0, block number=0, partition=0.
Tape block size 0 bytes. Density code 0x8c (EXB-8505 compressed).
Soft error count since last status=0
General status bits on (41010000):
BOT ONLINE IM_REP_EN

And I also checked the switches at the bottom of the tape drive. Only switch 3 is off.

[Vincent Farrugia]

Hello,

Check your data. If it is already compressed, the tape cannot compress it further, yielding to the famous 12Gb mark. Natively, that's how much a DDS3 tape can hold.

HTH,
Vince

[Sven Jacobsen]

HI Alvin,

Vincent is right. It all looks like you are having compressed data already. That kind of data wil only get bigger in size when being backed up, as the data itself will not shrink in size but another index for decompression is written anyway. To check if that is the case I would suggest the following:
You have already been talking about the switches on the bottom of the drive. THe switches 1. Compression on/off and 2. Host intervention should be switched off. That would ensurer that there is definetly no hardware compression performed by the drive. Now you should get the 12gb on the tape. Unfortunately that does not solve our problem but it gets you a proof that your drive is ok and you might get the data on 2 tapes instead on 3 tapes like right now.
The only solution for your situation would be the usage of another drive with enough capacity. Right now I would suggest a VS80 drive using DLT1 technology. It gets you 40gb uncompressed on one Tape and is better in price/performance relation than most of the other drives in that class. DDS4 drives only put 20gb on one tape, so your data would not fit one tape either, especially because the data amount is probably growing.