[Info-vax] Getting tape drive errors make no sense

[AEF]

On Friday, October 25, 2013 3:33:26 PM UTC-4, tadamsmar wrote:
> I tried to copy a large save-set (a full disk backup) from tape to a large disk.  That is I am just trying to copy the file from tape to disk, not trying to restore a volume.
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> The save-set was created and verified on a DDS3 tape on a DDS3 drive. One of those 12/24 GB DAT drives that are common on Alpha DS10 466 mhz systems.
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> I was trying to copy it using a DDS4 hotswap drive on a Alpha DS10 617 mhz system.
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> Both systems have disk shadow sets with 2 members.
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> I got errors when I tried to copy.
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> I did a search of the file and also got parity errors.
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> I tested the tape on a 3rd system with a DDS3 drive (similar system that wrote the tape).  I could search it there with no errors.
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> (I was using searching instead of copying as a test case because the 3rd system did not have big disks that would allow copying the whole file.)
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> The DDS4 drive is backward compatible to DDS3. I does incrementals every night to a DDS3 tape and it's disk backups are done with DDS3 tapes.  I cleaned the drive after the errors, but it shows no need be cleaned when it does the incrementals.
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> I will probably see if the DDS4 drive can search one of the savesets that were created on it on Monday.  Maybe I need to do this kind of stress test to sort things out.
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> Some of my tests indicate that it's not hitting the parity errors at the same point on the tape.  I tried copying the file twice and it got farther the second time before it had a parity error.

I had a similar problem. I had 4mm DAT tapes, DDS-2, that would get parity 
errors on TLZ07 drives, and not always in the same place. Different drives 
would do better or worse on the same tape. My solution? I stopped using DDS-2 
and switched to DDS-1. Worked like a charm. 

Perhaps you have a head-alignment mismatch. I had one tape drive that could 
only read tapes made on itself and not tapes made on any other drive. 

AEF