What Performance Tuning Manual are you refering too?

I am not sure of the maximum number of volumes but you SHOULD define more
than one volume for the database, and put these volumes on separate disks
because it allows simultaneous access to different parts of the database.
Also, if you want to really use disk space efficiently, allocate a few large
disk volumes rather than many small disk volumes. You can avoid losing space
to the overhead processing that TSM does.

Regards,

Demetrius