Other than lowering the backup process prioritys another way to cause TSM
to use less resources is to set 'MEMORYEFFICIENT YES' in the options.
This will cause TSM to use less memory, and also slow down it's disk
scanning.

Also check TSM's 'copy group' serialization parameters, the default of
'shared static' could cause a file in use by an appliation to be backed up
4 times before giving up.  It may be better to use 'static' or 'dynamic'
to reduce the amount of disk activity during a backup at the expense of
having 'fuzzy' backups.

Finally, from what I have seen, many appliation servers are normally quite
idle and not doing anything cpu/disk/network at all, even 24x7 ones.  It's
the 'backup' that uses the most cpu/disk/network Just because it has to
scan all the files every day, and this happens to be more than the
application server does in a day.

So the 'performance monitor' spike during the backup and people perceive
this as a problem, when really it is not.

Matt G.