I have a Dell Powervault 100T DAT drive. Although this is badged as Dell I think it is in fact a Seagate unit.

The drive is about 4 years old.

When backing up it has started taking forever with a lot of streaming, stopping, rewinding and then streaming again. I have tried cleaning and new tapes but the same thing happens.

Now I have discovered that if I use mt -f /dev/st0 erase on a tape the backup runs smoothly.

AFAIK there is no specific formatting on these tapes so I can only assume that the erase command retensions the tape.

Is there is a quicker way to retension a tape than a full erase? I have tried mt -f /dev/st0 retension but nothing happens.

When you say new" tapes what do you mean? New as in "new to you and the drive" or new as in "still in the cellophane wrapper?"

DAT drives are like mini VHS video recorders in that they wrap the tape round the read/write head drum which spins at an angle writing data stripes diagonally across the tape. Exabyte drives are the bigger version.
Like VHS video recorders you can suffer from tracking errors so I reckon your erase is actually matching the tape back up to the drive. Your stop/rewind/start backups implies that the drive is having problems writing the data, you'd get this by using tapes written on a different slightly misaligned drive.

Hope this helps!

Play Bonny!

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Firstly many thanks for your response.

New as in "still in the cellophane wrapper?". Even the old tapes have only been used within this drive but maybe I haven't been as careful with them as I should have been?

I read on another forum that it is quicker to fill the tape with data rather than erase it but haven't found any command line utilities that will do it (perhaps write a script that repeatedly appends a 1Mb file to the tape?).

I am only using tar, mt and tapeinfo. Are there any other commands I should be researching?

Thanks again

I can't think of any off the top of my head. The only other reason I can think of which would do the stop/rewind/start type of writing is if the files you are backing up are very short. Each file has to be written individually and the tape re-positioned to allow it to accelerate to the correct speed before writing the next file. (I come from the era of old DEC TU10 reel-to-reel tape drives with vacuum tensioning where it was very noticeable!) If the backup was perhaps one large compressed file where the data was streamed, it would run more smoothly.
No... Don't ask me how to organise that.

Play Bonny!

Okay, thank you for your insight!

Some of the files are very small (emails in maildir format) but I would expect to see the same problem after erasing the tape. I think you are right with the alignment issue though.

I will try to perform an erase cycle on every new tape and thereafter on every 5 uses of the tape and see how that goes.