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LTT "Data on tape (average): Warning"

LTT "Data on tape (average): Warning"

After running a full media test I get the message:

Data on tape (average): Warning

What is this trying to tell me please?

A "Data Assessment Test" on the same tape says "Great Margin" ....

Thanks, Dave


Valued Contributor

Re: LTT "Data on tape (average): Warning"

Those are two different measures.  During writing the drive reads immediately after writing and measures the signal.  If it determines that the signal is not good enough then it writes the data again until it reads back a really strong signal so that it knows the tape can sit on a shelf for many years and still be readable.  Rewriting the data takes physical space and there is some extra tape in the cartridge so that normally you still get the advertised capacity. 

The Data On Tape warning is reporting that there were more rewrites than usual

The Data Assessment test ignores the rewrites and looks at the signal quality of the data sets that are read back

A combination of messages like this means that the drive had trouble writting the data to the quality that it requires but that once the data was written it was written with high margin.

Tape drives are very conservative and always writing with high margin is the priority.

The question now is why the drive was having trouble writting.  It could be that there are problems with the tape or the drive may be worn out.  A quick test is to use several tapes of different ages (nearly new, good used, old) and run the Drive Assessment test.

Re: LTT "Data on tape (average): Warning"

Is there any way to get the "Data on tape (average)" for a cartridge without running an LTO Media Assessment Full Tape Test?

I want to re-check the condition of some tapes and if I can do it quickly rather than having to wait 2.5 hours per tape that will save lots of time.

PS From one of my other threads I think all the tapes showing a warning condition for this had been over-heated!

Thanks lots, Dave

Valued Contributor

Re: LTT "Data on tape (average): Warning"

I think that specific message only comes out of the test but if you write a reasonable amount to the tape and then pull a support ticket then look in Device->Drive Health->Drive->Write you can see the results for the most recent writes presented as a "margin".  The margin that the test is referring to is measured from several characteristics including those the capacity that the media assessment test uses and too much lost capacity will push the margin towards 0.

I'd recommend writing a pretty large block like 50-100GB.  Media damage from temperature can be broadly scattered over the whole tape or localized to areas of the media depending on how it happened.