Solaris Disk Slice Numbering
The root partition on a Solaris system is defined as Slice 0, and is mounted as root (/). This is the top level of the filesystem. In computer parlance root starts at the top, but if you look at it as a biological tree is grown, from the bottom up, it also makes sense as the origin of the filesystem.
Slice 1 is used for swap space, which is virtual memory. Some operating systems, like Windows, use a swap file, while UNIX and UNIX like filesystems use an entire partition for swap. The size of swap is reliant on how much physical memory is in the system. There are various formulas for how large to make the swap area. Some go for twice to twice plus half of physical memory, and some prefer larger in case physical memory increases. You can always add extra swap partitions in the future if they are needed.
Slice 2 is representative of the entire disk and is not mounted as anything.
Slice 3 is mounted as /export in the default setting. Directories exported via NFS, such as user HOME directories, are kept here.
Slice 4 is mounted as /export/swap. This is meant to provide virtual memory for client computers. It can also be mounted as /opt for optional software.
Slice 5 is usually mounted as /opt, for optional software that is not critical to the functioning of the system. If /opt is on Slice 4 then /var is what resides on Slice 5.
Slice 6 is mounted as /usr, which contains libraries and binary files that are used by regular system users. The /usr partition is shared between systems.
Slice 7 is mounted as /home, /export home, or /export/share. This holds user home directories or other shared data.
