I think I stumbled on something today. It appears that all of my NSS
volumes have a 4K block size. This must me set as default. Our EMC has a
128K element size (I think this is block size). My LTO3 uses 64K block

Are these mismatches the root cause of my slow backups, and other
performance problems I may be having with NSS?

What would be the recommended block size, and can I change it now?