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New LTO2 tapes unable to store more than 200gb ?

Posted on 2009-07-13
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Last Modified: 2012-05-07
Hi there,

I recently bought some more LTO2 tapes for our nightly backups, however the new tapes do not hold more than around 197-202gb.

The normal tapes I am currently using are TDK tapes, and are backing up about 230gig at a compression ratio of 1.33.  So it seems the drive, Arcserve and compression is all working good.
I recently bought some FujiFilm tapes and running the exact same nightly backup job, the job  stops at about 197gb and Arcserve requests the next tape.
I assumed it was the brand of tape so I bought some Sony tapes, but these also stopped at about 201gb.
Thinking that maybe this drive has some sort of relationship with TDK tapes, I bought a new box of them, and these new TDK tapes stop at about 203gb.

Ive formatted the tapes as normal, compression is "on" and the block size is the same on all the tapes.
Have I missed something simple here ?
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Question by:PhilCade
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by:ComputerTechie
ID: 24840032
I would do a firmware update for the tape drive also i would make sure your are running the most updated version of Arcserve.

It would like it not recognizing the tape correctly.

CT
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SelfGovern earned 500 total points
ID: 24850097
Are you backing up the exact same data now as you were when you were getting 230GB/tape?

200GB is the native capacity of an LTO-2 tape.  If you got more data than that on a tape, it's because your data was somewhat compressible.

If you are NOT getting more than approximately 200GB on a tape ("approximately" because there is some overhead in metadata stored with the actual data written to tape) it could be because of:
1) The files being sent to the tape is already compressed.  Some data types, like zip files, jpeg, mpeg, etc. are already compressed.  With few exceptions, well-compressed data can not be compressed further.
2) The data being sent to the tape is uncompressible.  Compression finds patterns in the data and replaces those patters with shorter tokens that can be used to restore the original data later.  Certain data, for instance, encrypted files, will not compress because there are no patterns in the data.
3) The data stream is being compressed or encrypted on the server (also known as software-compression or -encryption).  Either of these defeats the drive's ability to compress data.
4) The backup application has compression turned off -- but you have said that this is not the case.
5) I suppose it's possible that your tape head is starting to get dirty, which is causing significant additional space to be used to compensate for bad writes.  Normally you'd notice the 'clean drive' light, and perhaps get a signal in your backup application.
6) A (pending) failure in the tape drive -- Possible that the tape heads are starting to wear and there's additional error correction that has to be done in the writes; or, some other HW failure of the drive.

That's all well and good, but you're probably wondering what you can do about it.

If you have an HP tape drive, you can download the free HP Library and Tape Tools (L&TT)
from http://www.hp.com/go/tape -- see the link under "value added features".   In L&TT are
a variety of tests that I recommend you run:
1. Tape Drive diagnostics -- make sure that your tape drive is healthy.  If it reports failures, you can generate a support ticket and send it to HP to help the warranty process.
2. Data tests: You can read the actual data of the backup job and verify how compressible it is (or isn't).
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Author Comment

by:PhilCade
ID: 24902683
ComputerTechie: Ive updated the drivers and the firmware, but sadly this hasnt made any improvements :-(

SelfGovern: Thanks for the info. Yes, I am backing up the exact same data as this is the main file server.
It was suggested to me that the old tapes work better because they have not been wiped and are simply overwriting the data back to the same blocks, and that I should `erase` not just format an old working tape and see if the backup still works on this. I did this and the backup then failed at 220gb (230gb is a full working backup on normal old tapes)
Because this failed its now been suggested that the drive may simply be dirty, so I ran the cleaning tape again but the next backup on a new tape also failed.
This leads me to believe the drive may be faulty after all....
The drive is a Quantum/Certance, I downloaded and run the xTalk Console diagnostics software, and this has now thrown up an error on one of the tests :
"LTO Error Rate Test  -------- : Failed"

Ive since been advised this still may be dirty drive issue, so Im going to order a new cleaning tape, give that a whirl and try again. Fingers crossed.
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by:ComputerTechie
ID: 24906297
It also could be a cable issues.
when the tape drive moves it triggers.

CT
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Author Comment

by:PhilCade
ID: 25021195
At last, I eventulay get the Tape Drive replaced while the old one is off to repair/clean and everything is working back to normal.
The drive head must simply be worn out or too dirty to be cleaned with regular Cartridge Cleaners.
Im still a little confused to why the old tapes worked fine but the new ones wouldnt, but hey, the problem is now solved. !
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by:ComputerTechie
ID: 25025143
The older tapes might have a stronger magnetic field on the tape and it might need a factory firmware update to read new tapes.
Gland to hear it fixed for now.

CT
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