determining vxdg free space

Hi,

How do I determine the free space below?

[local ~]# vxdg -g msb_db_dg free
DISK DEVICE TAG OFFSET LENGTH FLAGS
msb_db_dg01 sdb sdb 312475648 316571392 n

Please help, I need to increase the file system of mysql folder on red hat ent 4 with vxfs.

Thank you!