Yes grub is a bootloader. Should be able to configure it to get the options you want.

A raw disk has a load of bytes on it. Partitions (or slices) are subdivisions of that space. A filesystem lives normally in a partition(or slice). A disk can have one single partition. A filesystem must be of some format and use a driver/handler.

In order to use a disk it has to be brought online, this is called "mounting" and basically identifies the type of filesystem, where the bytes for it are, what driver to use and where it should appear in the global file system (the mountpoint). When you want to take a disk offline it must be dismounted, hence "umount". A volume should be dismounted cleanly to make sure all buffers are flushed and files are closed. (see "sync").

"/etc/vfstab" is a file on Solaris which lists your volumes so the system can automatically mount them.