DAT - Hardware compression DAT

[Andersen]

Hello. I am using DAT72 and TapeWare as backup system. Recently I have become rather close to some 36GB to backup, and TapeWare starts returning Warning 1301 and Error 1303 because of the drive having problems writing.

It says: "Your tape drive is having problems writing data. No data has been lost but there has been a reduction in the capacity of the tape."

When I reduce the size of the set, the error does not appear. I dont use compressed partitions, hardware compression is ON at the drive and in TW advanced option and the Compression type is "System" so I would expect some significant headroom on top of the 36GB (uncompressed capacity) of the drive.

This appears not to be tha case. Can anyone please give me a hint on what is wrong?

Thanks for reading and replying.

[Torsten.]

Best idea would be to use LTT, do an assessment test and pull a support ticket for review.

http://www.hp.com/support/tapetools

[Andersen]

Thanks for the proposal. Attached LTT html-report taken immediately after Drive Assessment Test.

[Andersen]

... followed by a LTT html-report taken immediately after Data Compression Test.

During this test a compression factor of above 2 is found where the compression factor in the Drive Assessment Test report above is below one.

If these figures are correct I may be better served turning hardware compression off in daily use!

From my experiences with software compression tools much of the data - roughly 50% - can be compressed by a factor 4:1. So I expect the DAT72 drive to be able to store more than what I see here.

Thanks again, and hope someone can guide me to a solution.

[Torsten.]

Can you please attach the original lzh file?

[Andersen]

A LTT data .lzt file created immediately after a Drive Assessment Test is attached. Thanks for your support.

[Víctor Cespón]

Mixed results...

Device Analysis : Failed
Serial EEPROM Data is not accessible on this drive
Write (last 8 tapes) : Good Margin (62.2 GB)
Read (last 7 tapes) : Good Margin (39 GB)
Load/unload life : Great margin, 97% life remaining
Write Compression Ratio : 1.2:1 (last 32.5 GB)
Read Compression Ratio : 1.2:1 (last 29.2 GB)
Power on time : 180 days, 9 hours, 0 minutes
Load/Unload cycles : 234 (2% of expected life)

[Trygve Henriksen]

How old are the tapes?

DAT tapes are VERY fragile and(in my experience) prone to stretching. Also, tapes used in one drive was often found to be unreadable in another.
(Its over a decade since we scrapped our last DAT drive and went for DLT, then SDLT, and these days LTO4.)

[Andersen]

I would say that some of the tapes may have been written to some 50 times and we use full validation so those of the tapes may have been "rolled out" 100 times. If it is tape wear - is there a recommended lifetime?

[Trygve Henriksen]

Well, my preferred 'lifetime' for DAT is the amount of time it takes me to bin them, but that's my opinion.

50 times may be 'cutting it close' so to speak.
We used sets of 20 tapes back then, with a 4 week rotation, and occasionally swapping out a tape to store off-site as monthly, quarterly or yearly backup, and tapes that wasn't rotated generally got junked after 2 - 3 years at the max.
(Each tape was used 12 or 13 times/year, so... )

The problem is that the tape is so thin and narrow that it takes almost nothing to stretch it.
The 'almost nothing' in this case being the speed modern DAT drives use, combined with rapid spooling back and forth, particularly when doing a restore...

I think there was once systems that used VHS tapes, which were less reliable than DAT...
(8mm video tapes just about tied with DAT)