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What happens when unloading media of DLT8000?

Mi_Su
Occasional Contributor

What happens when unloading media of DLT8000?

Many unload timeout failures happen on different DLT8000 drives.

What happens when unloading media of DLT8000?
What is root cause of this unload timeout problem?

I guess that the root cause for most of timeout failures is damaged directory of the tape.
Because the updated directory is written back on the unload.

3 REPLIES
Marino Meloni_1
Honored Contributor

Re: What happens when unloading media of DLT8000?

you are right, a directory is written when you eject the tape.
But usualy if the read/write process work well, the directory write also work well.

If you manage your drive with a backup sw, this sw set the drive in reserved mode before to start writing on it, and if this task do not finish and the "reserved mode" bit is not cleared, when you try to unload the tape, this operation will not be allowed and you may receive time-out for this operation
Arend Lensen
Trusted Contributor

Re: What happens when unloading media of DLT8000?

Be aware that if you manage to get the tape out without it was able to write the directory, at the next load it will see that it has no directory. What it does then is read the whole contents of the tape and create that directory, this may confuse backup applications as they expect a drive to be online after lets say 1 minute. Recreating a directory can take many minutes...
Curtis Ballard
Honored Contributor

Re: What happens when unloading media of DLT8000?

The maximum unload time for a DLT8000 drive is 15 minutes. That occurs when you have a calibration failure on the last write followed by 3 successive calibration failures on the directory write attempt. The drive will then give up and unload the tape.

For this to happen you need one of three things:
A very dirty drive (how I tested this)
A bad tape
A bad head

Most of the time I see the longest unloads when there is a calibration failure on the last unload and then it takes 1 retry to write the directory and then the unload is around 5-7 minutes. There are a few corner cases where the unload will take 20 minutes or never finish but usually if it takes longer than 15 minutes then the drive has a dropped leader.