You can decrease the size of the file system using
fsadm, even while the file system is mounted.
Note In cases where data is allocated toward the end of the file system, shrinking may not be possible. If a file system is full, busy, or too fragmented, the resize operation may fail.
To decrease the size of a VxFS file system
fsadm [-b newsize] [-r rawdev] mount_point
The following example shrinks a VxFS file system mounted at
/ext to 20480 sectors.
To shrink a VxFS file system
fsadm -b 20480 /ext