On 26/09/12 22:37, Stephen Thompson wrote:
> I think I pointed this out before, but I also have used and new tapes 
> with 400-800Gb on them. It seems really hit or miss, though the tapes 
> with 400Gb or less are probably a 1/3 of my tapes. The other 2/3 have 
> above 400Gb. 

If you have small blocking factors and a lot of small files it's 
possible that bacula overheads are high (it reports actual data on tape, 
not data+overheads)

In my experience, tapes which achieve high compression factors are 
usually full of incremental backups containing highly repetitive data 
such as logfiles.


Tape capacities are quoted in Gb = 1*10^9, while bacula uses GiB for its 
reporting, but the kind of underrun you're seeing can't be entirely 
explained by that small difference.

I've occasionally seen LTO5 tapes marked as full when they're well short 
of expected capacity but this generally happens on a drive which is 
about to request a cleaning tape. Marking them as append has a 50:50 
chance of allowing them to continue and generally they're fine when 
recycled.

Have you tried btape to test the tape in question, or used dd to see how 
many bytes are actually on the tape? Smartctl will help too.





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