You can use the vxassist command to create and change volumes. vxassist is an automated one-step interface to Volume Manager
tasks. Unlike some Volume Manager commands, vxassist does not require a thorough understanding of Volume
Manager concepts.
vxassist can do tasks that would otherwise require the
use of several other Volume Manager commands. vxassist automatically performs all underlying and related
tasks that would otherwise be done by the user (in the form of other
commands).
vxassist does not conflict with existing Volume Manager
commands or preclude their use. Objects created by vxassist are compatible and inter-operable with objects
created by other Volume Manager commands and interfaces.
vxassist performs these tasks:
finds space for and
creates volumes
finds space for and creates mirrors for existing
volumes
finds space for and extends existing volumes
shrinks existing volumes and frees unused space
provides facilities for the online backup of existing
volumes
provides an estimate of the maximum size for a new
or existing volume
changes a volume's layout
For detailed information about how to use vxassist, refer to the vxassist(1M) manual page.
Advantages of using vxassist include:
The use of
vxassist involves only one step (command) on the part of the
user.
You are required to specify only minimal information
to vxassist, yet you can optionally specify additional parameters
to modify or control its actions.
vxassist tasks result in a set of configuration changes
that either succeed or fail as a group, rather than individually.
Most vxassist tasks work so that system crashes or other interruptions
do not leave intermediate states to be cleaned up. If vxassist finds an error or an exceptional condition, it
exits without leaving partially-changed configurations. The system
is left in the same state as it was prior to the attempted
vxassist task.
How vxassist Works |
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The vxassist command allows you to create and modify volumes.
You specify the basic volume creation or modification requirements
and vxassist performs the necessary tasks.
vxassist obtains most of the information it needs from
sources other than your input. vxassist obtains information about the existing objects and
their layouts from the objects themselves.
For tasks requiring new disk space, vxassist seeks out available disk space and allocates it
in the configuration that conforms to the layout specifications
and that offers the best use of free space.
The vxassist command typically takes this form:
vxassist keyword volume_name [attributes...] |
where keyword selects the task to perform. The first argument after
a vxassist keyword is a volume name, which is followed by
a set of attributes. For details on available vxassist keywords and attributes, refer to the vxassist(1M) manual page.
vxassist creates and manipulates volumes based on a set
of established defaults, but also allows you to supply preferences
for each task.
vxassist Defaults |
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vxassist uses a set of tunable parameters that can be specified
in the defaults files or at the command line. The tunable parameters
default to reasonable values if they are not listed on the command
line. Tunables listed on the command line override those specified
elsewhere. Here are the tunable parameters:
Internal defaults—The
built-in defaults are used when the value for a particular tunable
is not specified elsewhere (on the command line or in a defaults
file).
System-wide defaults file—The system-wide
defaults file contains default values that you can alter. These
values are used for tunables that are not specified on the command
line or in an alternate defaults file.
Alternate defaults file—A non-standard
defaults file, specified with the command vxassist -d alt_defaults_file.
Command line—The tunable values specified
on the command line override any values specified internally or
in defaults files.
Defaults File |
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The default behavior of vxassist is controlled by the tunables specified in the /etc/default/vxassist file. The format of the defaults file is a list
of attribute=value pairs separated by new lines. These attribute=value pairs are the same as those specified as options
on the vxassist command line (refer to the vxassist(1M) manual page for details).
Here is a sample vxassist defaults file:
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# by default:
# create unmirrored, unstriped volumes
# allow allocations to span drives
# with RAID-5 create a log, with mirroring don't create a log
# align allocations on cylinder boundaries
layout=nomirror,nostripe,span,nocontig,raid5log,noregionlog,
diskalign
# use the fsgen usage type, except when creating RAID-5 volumes
usetype=fsgen
# allow only root access to a volume
mode=u=rw,g=,o=
user=root
group=root
# when mirroring, create two mirrors
nmirror=2
# for regular striping, by default create between 2 and 8 stripe
# columns
max_nstripe=8
min_nstripe=2
# for RAID-5, by default create between 3 and 8 stripe columns
max_nraid5stripe=8
min_nraid5stripe=3
# create 1 log copy for both mirroring and RAID-5 volumes, by
default
nregionlog=1
nraid5log=1
# by default, limit mirroring log lengths to 32Kbytes
max_regionloglen=32k
# use 64K as the default stripe unit size for regular volumes
stripe_stwid=64k
# use 16K as the default stripe unit size for RAID-5 volumes
raid5_stwid=16k
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