[Bacula-users] Trying to understand block sizes.

I am just trying to understand things, so please bear with me.  I 
understand that the recommended block size is 256K.

I thought that earlier this week, I tested the LTO-3 drive with a 1M 
block size.  But attempting to do so again, does not work.  So now it 
looks like the actual maximum block size for the drive is 512M(524288).  
So now my questions.

#dd if=/dev/zero of=/dev/nst1 bs=524288 count=1
This completes successfully.

If I set the Maximum Block Size = 524288 in the sd, and run btape test,
This fails.  Why?

If I set the Maximum Block Size = 523264 (1024 less) in the sd,  and run 
btape test,
This succeeds.  Why?

If I round this block size to a 4096 division, it would be 520192.
If I set the Maximum Block Size = 520192 in the sd, and run btape test,
This succeeds, but it says it is using a 520092 block size  Why?




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