The growfs(1M) command expands a UFS file system without loss of service or data. H`owever, write-access to the metadevice is suspended while the growfs(1M) command is running. You can expand the file system to the size of the slice or the metadevice that contains the file system.
The file system can be expanded to use only part of the additional disk space by using the -s size option to the growfs(1M) command.
When expanding a mirror, space is added to the mirror's underlying submirrors. Likewise, when expanding a trans metadevice, space is added to the master device. The growfs(1M) command is then run on the mirror or the trans metadevice, respectively. The general rule is that space is added to the underlying devices(s), and the growfs(1M) command is run on the top-level device.