Installation guide
structure of LSM objects to organize and optimize disk usage and guard
against media failures. The structure is built with the objects in the
following logical order:
1. Subdisks
2. Plexes (mirrors)
3. Volumes
Each object has a dependent relationship on the next-higher element, with
subdisks being the lowest-level objects in the structure and volumes the
highest level. LSM maintains a configuration database that describes the
objects in the LSM configuration and implements utilities to manage the
configuration database. Multiple mirrors, striping, and concatenation are
additional techniques you can perform with the LSM objects to further
enhance the capabilities of LSM.
Table 8–2 describes the LSM objects used to represent portions of the
physical disks.
Table 8–2: LSM Objects
Object Description
Volume Represents an addressable range of disk blocks used by applications,
file systems, or databases. A volume is a virtual disk device that looks
to applications and file systems like a regular disk-partition device. In
fact, volumes are logical devices that appear as devices in the /dev
directory. The volumes are labeled fsgen or gen according to their
usage and content type. Each volume can be composed of from one to
eight plexes (two or more plexes mirror the data within the volume).
Due to its virtual nature, a volume is not restricted to a particular
disk or a specific area thereof. You can change the configuration of a
volume (using LSM utilities) without disrupting applications or file
systems using that volume.
Plex A collection of one or more subdisks that represent specific portions
of physical disks. When more than one plex is present, each plex is a
replica of the volume; the data contained at any given point on each
is identical (although the subdisk arrangement may differ). Plexes
can have a striped or concatenated organization.
Subdisk A logical representation of a set of contiguous disk blocks on a
physical disk. Subdisks are associated with plexes to form volumes.
Subdisks are the basic components of LSM volumes that form a
bridge between physical disks and virtual volumes.
8–4 Administering the Logical Storage Manager