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VxVM VolumesVxVM uses logical volumes to organize and manage disk space. A volume is made up of portions of one or more physical disks, so it does not have the physical limitations of a physical disk. A volume can provide greater capacity and better availability and performance than a single physical disk. A volume can be extended (grown) across multiple disks to increase capacity, mirrored (copied) on another disk to provide data redundancy, and/or striped across multiple disks to improve I/O performance. You can use VxVM to create the following types of volumes:
A concatenated volume is made up of one or more disk regions that are linked together (concatenated) in a linear fashion. A concatenated volume can consist of disk regions on multiple disks; a concatenated volume that extends across two or more disks is also known as a spanned volume. Note Data in this type of volume cannot be recovered if the underlying disk fails. However, a concatenated volume can be mirrored (copied) onto other disks to protect its data against disk failure. Striped volume data is interleaved (striped) across two or more physical disks. Striped volume data is spread across the disks alternately and evenly in small, equal-sized portions of data called stripe units. Striping improves performance. Note Data in this type of volume cannot be recovered if one of the underlying disks fails. However, a striped volume can be mirrored (copied) onto other disks to protect its data against disk failure. RAID-5 volume data is interleaved (striped) across three or more physical disks. Within each stripe across the set of disks, the data on one of the disks is parity data. If one of the physical disks fails, the parity data can be used to reconstruct and recover the lost data. Note RAID-5 volumes cannot be mirrored.
Volumes with concatenated or striped layouts can be mirrored to increase data availability. All of the data in a mirrored volume is duplicated on at least one other physical disk. If one of the disks fails, the data can still be accessed from one of the remaining disks. The plexes in a mirrored volume typically have the same layout, but a volume can consist of plexes with different layouts. A mirrored volume has a “mixed” layout if the plexes in the volume have different layouts. A layered volume is built on one or more other volumes. The underlying volumes are typically mirrored. In layered volumes, mirroring is done at a lower level and with smaller granularity than with non-layered volumes, so each mirror covers a relatively small storage region. Layered volumes tolerate disk failure better than non-layered volumes and provide improved data redundancy. If a disk in a layered volume fails, only a portion of the redundancy is lost and recovery time is usually quicker than it would be for a non-layered volume. Layered volumes also reduce the chance that two disk failures will result in lost data. The underlying volumes in a layered volume are used exclusively by VxVM and are not intended for user manipulation. With VxVM, you can create the following types of layered volumes: The following table summarizes the advantages and disadvantages of each volume layout. Note The total volume size you indicate for the volume in the Create Volume Wizard is the usable size for storing the data. Depending on the layout type, the volume can take more space on the disk. The size shown in the Wizard for simple, striped, and spanned volumes is the actual volume size on the disk. A RAID-5 volume requires additional space for parity information, and a mirrored volume is a multiple of the space taken by the original plex of the volume. The Wizard provides a Query Max Size button to determine the size of the volume. Again, this is the usable size of the volume rather than the actual size taken by the volume on the disk. |
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