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Why would brand new LTO3 tapes hold less and write/read slower than old tapes in current inventory?

Posted on 2011-02-10
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I'm using Backup Exec 11d (Rev 7170, HotFix 37, Svc Pk 5, HotFix 70 using BE drivers) and a Quantum Superloader3 w/ Quantum drive (ver 2181).  All new media (Quantum and Fuji) I use will give me "Media Full" between 232GB and 308GB while media created in 2009 will get 'full' between 438GB and 496GB backing up the same data using the same jobs.  My weekend backup (just over 1TB) should be using 3 tapes and now is up to 5.  One of my nightly backups typically (on old tapes) runs 4 hours. Last night on new tapes... 7 hours 20 minutes which ran over my next backup job start time.  I have xTalk logs for Device Health and write/read full tape on a 'New' tape.  I need to run write/read full tape on an old tape for comparison.
Any help, greatly appreciated. Thanks.
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Question by:cfox869
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by:scriven_j
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LTO 3 tapes should be 400GB capacity (800GB using compression) so this is a bit of a strange one.

Probably worth updating the Quantum Superloader firmware.

Did you do an erase or anything on the tapes before you started using them?

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by:scriven_j
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I use Netbackup and LTO3, but tapes show as full at around 600GB.
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by:scriven_j
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I have just looked historically and some say they are full as low as 480GB and as high as 728GB (we use compression) - so if you halved those (assuming you aren't using compression), the range is pretty similar to what you are seeing.....
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by:Gerald Connolly
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LTO2 = 200GB Uncompressed
LTO3 = 400GB Uncompressed

If you are now only getting 200GB on a tape are you sure they are LTO-3 tapes?

What does BackupExec think they are?
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SelfGovern earned 500 total points
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Have you tried to re-use one of those old tapes that had gotten over 400GB, to see if you still get over 400GB on it?  If not, my expectation is that you either have a tape head that has been used to the extent of its useful life, or, that it's very dirty.

Each time the tape drive encounters a write error, it flags that area of the tape as bad and writes the current block over again.   If this happens enough, you notice it as a decrease in tape capacity.   It doesn't sound like you're seeing the cleaning light, so the most likely cause of this problem would be a used-up head.

It's also possible that the new tapes are fairly "dirty" -- it's common for new tapes to have loose bits of magnetic particles on them... cheap media or a bad batch will have more loose bits than better-quality media.   And if that isn't enough, new media is, essentially, a cleaning tape... so if you haven't used new media in quite a while, this new set may be scraping bits off the head and the loose material may be causing errors that contribute to soft write errors.

SO -- If Quantum has any kind of diagnostics, I suggest you download and run some tests on the drive and the media.   That should give you more hard information about what the error condition might be.   You can also usually look in your backup application under the tape properties to see what kind of errors you've been getting.

Other possibilities: Tapes accidentally formatted as LTO-2.   Tapes with LTO-2 bar-code labels, which will cause a library to read and report them as LTO-2 media.  (rarely) LTO-2 tapes mislabeled at the factory.
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by:cfox869
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Update: Quantum is replacing the drive after reviewing the xTalk logs for Device Health and Full tape write/read on both "New Media" and "old known good media".

SelfGovern: Your assessment is correct.  "tape head that has been used to the extent of its useful life"  Thank you.

The attached file shows the tape capacity decline from March 2010.  And you can see the same decline from October 2008.  The tape capacity went back to 'normal' after the drive was replaced in Sept 2009.  



Date-and-Capacity-Page-2.jpg
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