What do people have set as "Reduce Fragment Size" for LTO3/4 tapes

We never had ours set, but a smaller value can improve the speed of restores especially for restoring a few smaller files in a large backup.

A quick search of the forum (for reduce fragment size) will yield 'a lot' of resolved posts, including a pointer to the following T/N (for 7.1 - not sure if there is a newer one):

http://www.symantec.com/business/support/index?page=content&id=HOWTO56051

In the end it comes down to your own environment & how your backups/restores are performing (ours were few & far between, so our emphasis was always on getting the data onto tape in the first instance).

Just remember fragment size determine how many data Netbackup minimum has to read to restore a single file. See it like a conveyor belt , where the fragment size is containers and tape the conveyor belt 

For database backup big frament is good

For file systems backup, smaller fragments is perferable, but will increase Netbackup catalog space slightly due to the larger mount of fragment pointers.