A RAID 0 volume is a volume built from slices or soft partitions, and is either used directly or as the basic building block for RAID 1 volumes (mirrors) and transactional volumes. There are three kinds of RAID 0 volumes: concatenated volumes, striped volumes, and concatenated striped volumes.
In practice, people tend to think of two basic simple volumes: concatenated volumes and striped volumes. (A concatenated stripe is a striped volume that has been "grown" from its original configuration by concatenating slices or created from scratch using the appropriate metainit command.)
Simple volumes enable you to quickly and simply expand disk storage capacity. The drawback to a RAID 0 volume is that it does not provide any data redundancy. A RAID 1 (mirror) or RAID 5 volume can provide data redundancy. (If a single slice fails on a RAID 0 volume, data is lost.)
You can use a RAID 0 volume containing multiple slices for any file system except the following:
Root (/)
/usr
swap
/var
/opt
Any file system accessed during an operating system upgrade or installation
Note - When you mirror root (/), /usr, swap, /var, or /opt, you put the file system into a one-way concatenation (a concatenation of a single slice) that acts as a submirror. This is mirrored by another submirror, which is also a concatenation.
A RAID 0 concatenated volume, or RAID 0 concatenation, is a volume whose data is organized serially and adjacently across disk slices, forming one logical storage unit.
You would use a RAID 0 concatenated volume to get more storage capacity by logically combining the capacities of several slices. You can add more slices to the RAID 0 concatenated volume as the demand for storage grows.
A RAID 0 concatenated volume enables you to dynamically expand storage capacity and file system sizes online. With a RAID 0 concatenated volume you can add slices even if the other slices are currently active.
Note - To increase the capacity of a RAID 0 (stripe) volume, you would have to build a RAID 0 concatenated stripe (see RAID 0 Concatenated Stripe).
A RAID 0 concatenated volume can also expand any active and mounted UFS file system without having to bring down the system. In general, the total capacity of a RAID 0 concatenated volume is equal to the total size of all the slices in the RAID 0 concatenated volume. If a RAID 0 concatenation contains a slice with a state database replica, the total capacity of the RAID 0 concatenation would be the sum of the slices less the space reserved for the replica.
You can also create a RAID 0 concatenated volume from a single slice. You could, for example, create a single-slice RAID 0 concatenated volume. Later, when you need more storage, you can add more slices to the RAID 0 concatenated volume.
RAID 0 Concatenations have names like other volumes (d0, d1, and so forth). For more information on volume naming, see Volume Conventions.
A RAID 0 striped volume, or stripe, is a volume that arranges data across two or more slices. Creating RAID 0 volumes alternates equally-sized segments of data across two or more slices, forming one logical storage unit. These segments are interleaved round-robin, so that the combined space is made alternately from each slice, in effect, shuffled like a deck of cards.
Note - Sometimes a striped volume is called a "stripe." Other times, "stripe" refers to the component blocks of a striped concatenation. "To stripe" means to spread I/O requests across disks by chunking parts of the disks and mapping those chunks to a virtual device (a volume). Creating stripes is also classified as RAID level 0, as is concatenation.
While creating RAID 0 stripes and concatenations both are methods of distributing data across disk slices, creating RAID 0 stripes alternates chunks of data across disk slices, while RAID 0 concatenation distributes data "end-to-end" across disk slices.
For sequential I/O operations on a RAID 0 concatenated volume, Enhanced Storage reads all the blocks on the first slice, then all the blocks of the second slice, and so forth.
For sequential I/O operations on a RAID 0 striped volume, Enhanced Storage reads all the blocks in a segment of blocks (called an interlace) on the first slice, then all the blocks in a segment of blocks on the second slice, and so forth.
On both a RAID 0 concatenation and a striped volume, all I/O occurs in parallel.
A RAID 0 concatenated stripe is a striped volume that has been expanded by concatenating additional slices (stripes).