Enhanced Storage lets you expand a existing volume by adding additional slices.
Mounted or unmounted UFS file systems contained within a volume can be expanded without having to halt or back up your system. (Nevertheless, backing up your data is always a good idea.) After the volume is expanded, you grow the file system with the growfs(1M) command.
After a file system is expanded, it cannot be decreased. Decreasing the size of a file system is a UFS limitation.
Applications and databases using the raw metadevice must have their own method to "grow" the added space so that the application or database can recognize it. Enhanced Storage does not provide this capability.
You can expand the disk space in metadevices in the following ways:
Adding a slice to a stripe or concatenation.
Adding multiple slices to a stripe or concatenation.
Adding a slice or multiple slices to all submirrors of a mirror.
Adding one or more slices to a RAID 5 volume.