XLV Logical Volumes

XLV Logical Volumes

The XLV Volume Manager provides these advantages when XLV logical volumes are used as raw devices and when EFS or XFS filesystems are created on them:

support for very large logical volumes--up to one terabyte on 32-bit systems and unlimited on 64-bit systems.
support for disk striping for higher I/O performance
plexing (mirroring) for higher system and data reliability
online volume reconfigurations, such as increasing the size of a volume, for less system downtime

However, using XLV logical volumes is not recommended on systems with a single disk.

With XFS filesystems, XLV provides these additional advantages:

filesystem journal records on a separate partition, which can be on a separate disk, for maximum performance
access to real-time data

When XFS filesystems are used on XLV volumes, each logical volume can contain up to three subvolumes: data (required), log, and real-time. The data subvolume normally contains user files and filesystem metadata (inodes, indirect blocks, directories, and free space blocks). The log subvolume is used for filesystem journal records. It is called an external log. If there is no log subvolume, journal records are placed in the data subvolume (an internal log). Data with special I/O bandwidth requirements, such as video, can be placed on the optional real-time subvolume.

XLV increases system reliability and availability by enabling you to add or remove a copy of the data in the volume (a plex), increase the size of (grow) a volume, and replace failed elements of a plexed volume without taking the volume out of service.

Converting from lv logical volumes to XLV logical volumes is easy. Using the commands lv_to_xlv and xlv_make, you can convert lv logical volumes to XLV without having to dump and restore your data.

EFS or XFS filesystems can be made on XLV logical volumes.

Composition of Logical Volumes
XLV Logical Volume Names
XLV Daemons
XLV Error Policy
XLV Logical Volume Planning
Real-Time Subvolumes