You can extend or shrink mounted VxFS file systems using the fsadm command. The size to which file system can be increased depends on the file system disk layout version. A file system using the Version 7 or later disk layout can be up to 8 exabytes in size. The size to which a Version 7 or later disk layout file system can be increased depends on the file system block size.
See About disk layouts.
See the format
(1M) and fsadm_vxfs
(1M) manual pages.