You can extend or shrink mounted VxFS file systems using the fsadm command. Use the extendfs command to extend the size of an unmounted file system. A file system using the Version 6 or 7 disk layout can be up to 8 exabytes in size. The size to which a Version 6 or 7 disk layout file system can be increased depends on the file system block size.

See About disk layouts.

See the fsadm_vxfs(1M) and fdisk(8) manual pages.