Creating Volumes

Basic—The basic approach takes information about what you want to accomplish and then performs the necessary underlying tasks. This approach requires only minimal input from you, but also permits more detailed specifications. Basic operations are performed primarily through the vxassist command.

Manual—The advanced approach consists of a number of commands that typically require you to specify detailed input. These commands use a "building block" approach that requires you to have a detailed knowledge of the underlying structure and components to manually perform the commands necessary to accomplish a certain task. Advanced operations are performed through several Volume Manager commands.

Concatenated—A volume whose subdisks are arranged both sequentially and contiguously within a plex. Concatenation allows a volume to be created from multiple regions of one or more disks if there is not enough space for an entire volume on a single region of a disk.

Striped—A volume with data spread evenly across multiple disks. Stripes are equal-sized fragments that are allocated alternately and evenly to the subdisks of a single plex. There must be at least two subdisks in a striped plex, each of which must exist on a different disk. Throughput increases with the number of disks across which a plex is striped. Striping helps to balance I/O load in cases where high traffic areas exist on certain subdisks.

RAID-5—A volume that uses striping to spread data and parity evenly across multiple disks in an array. Each stripe contains a parity stripe unit and data stripe units. Parity can be used to reconstruct data if one of the disks fails. In comparison to the performance of striped volumes, write throughput of RAID-5 volumes decreases since parity information needs to be updated each time data is accessed. However, in comparison to mirroring, the use of parity reduces the amount of space required.

Mirrored—A volume with multiple plexes that duplicate the information contained in a volume. Although a volume can have a single plex, at least two are required for true mirroring (redundancy of data). Each of these plexes should contain disk space from different disks, for the redundancy to be useful.

Striped and Mirrored—A volume with a striped plex and another plex that mirrors the striped one. This requires at least two disks for striping and one or more other disks for mirroring (depending on whether the plex is simple or striped). A striped and mirrored volume is advantageous because it both spreads data across multiple disks and provides redundancy of data.

Mirrored and Striped—A volume with a plex that is mirrored and another plex that is striped. The mirrored and striped layout offers the benefits of spreading data across multiple disks (striping) while providing redundancy (mirroring) of data. The mirror and its striped plex are allocated from separate disks.

Layered Volume—A volume built on top of volumes. Layered volumes can be constructed by mapping a subdisk to a VM disk or to a storage volume. A storage volume provides a recursive level of layout that is similar to the top-level volumes. Layered volumes allow for more combinations of logical layouts.