We have a DLT tape drive. Lately it wants to take 6-7 hours to do a backup instead of its usual two or less.  But not every night,  and not on the same night every week.  I have been putting in new tapes now, but it still occurs randomly. I have cleaned it. I can restore from the tapes no problem. It doesn’t appear to be fighting some nightly process for CPU cycles. Any ideas on what gives?

Giles Schipper replies

Something that may be causing extended backup time is excessive IO retries, as the result of deteriorating tapes or tape drive.

One way to know is to add the ;STATISTICS option to your STORE command. This will show you the number of IO retries as well as the actual IO rate and actual volume of data output.

Another possibilty is that your machine is experiencing other physical problems resulting in excessive logging activity and abnormal CPU interrupt activity — which is depleting your system resources resulting in extended backup times.

Check out the following files in the following Posix directories:

/var/stm/logs/os/*
/var/stm/logs/sys/*

If they are very large, you indeed may have a hardware problem — one that is not "breaking" your machine, but simply "bending" it.