Choose RAID 0 (Concatenation) to expand the capacity of an existing data set, such as a file system. Concatenation is good for small random I/O and for even I/O distribution, and appropriate for all file systems up to a Tb in size. You must use a concatenation to encapsulate root (/), swap, /usr, /opt, or /var when mirroring these file systems.
Choose a stripe to take advantage of the performance increases that come from accessing data in parallel and to increase capacity. Always use striped volumes for new file systems or data sets.
Creating a stripe enables multiple controllers to access data at the same time (parallel access). Parallel access can increase I/O throughput because all disks in the volume are busy most of the time servicing I/O requests. Creating a stripe is good for large sequential I/O and for uneven I/O.
Note that an existing file system cannot be directly converted to a RAID 0 volume. If you need to place a file system on a RAID 0 volume, you can back up the file system, create a RAID 0 volume, then restore the file system to the striped volume.
When creating a stripe, do not use slices of unequal size, as this will result in unused disk space.
Specifying Interlace Value
Interlace value specifies the size of the logical data chunks in a RAID 0 volume. In theory, different interlace values can increase performance for your configuration. The performance increase comes from several disk arms doing I/O. When the I/O request is larger than the interlace size, you may get better performance. However, unless you have concrete knowledge of both the hardware you are using and your software internals, you should either perform empirical testing on the system you will be using, or strongly consider using the default interface value of 16 Kbytes.
Choosing a RAID 0 Volume
A RAID 0 concatenated stripe is a set of two or more stripes that are then concatenated together for a larger logical volume, which provides both parallel access and larger size than a pure stripe could provide. Additionally, tThis is the only way to expand an existing striped volume.
When you create a RAID 0 volume of more than one slice, any slice except the first skips the first disk cylinder, if the slice starts at cylinder 0. This is to preserve the disk label in the first disk sector in all of the slices except the first. The metadisk driver must skip at least the first sector of those disks when mapping accesses across the stripe boundaries. Because skipping only the first sector would create an irregular disk geometry, the entire first cylinder of these disks is skipped. This enables higher level file system software (UFS) to optimize block allocations correctly. Thus, Enhanced Storage protects the disk label from being overwritten, and purposefully skips the first cylinder.
The reason for not skipping the first cylinder on all slices in the RAID 0 concatenation or stripe has to do with UFS. If you create a concatenated volume from an existing file system, and add more space to it, you would lose data because the first cylinder is where the data is expected to begin.