Installation guide

Table 8–4: LSM Configuration Options
Configuration Description
Concatenated
volumes
You concatenate multiple LSM disks together to form a big
volume. You can use a concatenated volume to store a large file
or file systems that span more than one disk. Disk
concatenation frees you from being limited by the actual
physical sizes of individual disks so that you can combine the
storage potential of several devices. Use the default disk group,
rootdg, to create a concatenated volume from the public
regions available. You can also add more LSM disks and create
volumes from the new disks you added.
Mirrored volumes You associate multiple plexes with the same volume to create a
mirrored volume. If you are concerned about the availability of
your data, then plan to mirror data on your system. You should
map plexes that are associated with the same volume to
different physical disks. For systems with multiple disk
controllers, you should map a volume’s plexes to different
controllers.
The volassist command will fail if you specify a device that
is already in the volume as the mirrored plex; the bottom-up
commands will not fail.
Striped volumes For faster read/write throughput, use a volume with a striped
plex. On a physical disk drive, the drive performs only one I/O
operation at a time. On an LSM volume with its data striped
across multiple physical disks, multiple I/Os (one for each
physical disk) can be performed simultaneously.
The basic components of a striped plex are the size of the plex
in multiples of the stripe width used, the actual stripe width,
and number of stripes. Stripe blocks of the stripe width size are
interleaved among the subdisks, resulting in an even
distribution of accesses among the subdisks. The stripe width
defaults to 128 sectors, but you can tune the size to specific
application needs. The volassist command automatically
rounds up the volume length to multiples of stripe width.
Administering the Logical Storage Manager 8–13