vgchange(1M)

NAME

vgchange — set LVM volume group availability

SYNOPSIS

Activate volume group

/usr/sbin/vgchange -a availability [-l] [-p] [-q quorum] [-s] [-P resync_daemon_count] [vg_name...]

Assign to high availability cluster and mark volume group sharable

/usr/sbin/vgchange -c cluster -S sharable vg_name

Remarks

MC/ServiceGuard cluster operations require the installation of the optional MC/ServiceGuard software, which is not included in the standard HP-UX operating system.

Lock Manager cluster operations require the installation MC/LockManager software which is not included with the standard HP-UX operating system.

Mirrored disk operations require the installation of the optional HP MirrorDisk/UX software, which is not included in the standard HP-UX operating system.

DESCRIPTION

The vgchange command with the -a option activates or deactivates one or more volume groups.

The vgchange command with the -c option controls the membership of one or more volume groups in a high availability cluster. The vgchange command with the -c and -S options control the membership of a volume group and mark it sharable.

The vgchange command without the -P resync_daemon_count option (default) will spawn one nomwcsyncd process for each NOMWC/NONE volume group being activated. This may create a lot of nomwcsyncd processes running concurrently when it activates a large number of NOMWC/NONE volume groups and overload.

The -P resync_daemon_count option provides a way to control the number of concurrent nomwcsyncd processes. The count is an advisory number and a different count might be chosen internally if load balance or other reason is needed. When specified, there are up to resync_daemon_count + 1 nomwcsyncd processes; one of them is the controlling processing to spawn others. -P 0 will use the system default (currently defined to be 4).

vg_name must be defined as a volume group in the file /etc/lvmtab. If vg_name is omitted, all volume groups defined in /etc/lvmtab are affected.

High Availability Cluster Overview

Volume groups can be defined on disk volumes that are connected to two or more systems in a high availability cluster. This situation has a high potential for data corruption unless special software is used to coordinate shared access to the same volume group by all systems. This coordination is provided by MC/ServiceGuard or MC/LockManager.

A volume group can be marked as part of a MC/ServiceGuard cluster. When such a group is activated in exclusive mode, it can be accessed for exclusive read-write activity by only one of the systems at a time; the other systems can have read-only access to the data.

A volume group can be marked as a part of an MC/LockManager cluster. In this case, the volume group can be marked as sharable, and may be activated in shared mode for read-write access by all the nodes in the cluster. Shared read-write access by multiple cluster nodes is coordinated by MC/LockManager's distributed lock manager (DLM).

Options and Arguments

vgchange recognizes the following options and arguments:

vg_name

The path name of a volume group.

-a availability

Set volume group availability. availability can have one of the following values:

y

Activate each specified volume group and all associated physical and logical volumes for read-write access. If a volume group is marked as part of a high availability cluster, it is activated in exclusive read-write mode, as for the -a e option.

e

Activate each specified volume group and all associated physical and logical volumes for exclusive read-write access. The volume group must be marked as part of a high availability cluster, and the availability software must be running on the system; otherwise, the volume group is not activated.

s

Activate each specified volume group and all associated physical and logical volume for shared read-write access. The volume group must be marked as part of a high availability cluster and marked sharable; otherwise, the volume group is not activated.

If any of the logical volumes in the volume group are mirrored, and if there are more than two systems in the high availability cluster, this volume group will not be activated because HP MirrorDisk/UX software is only supported in a clustered environment with a maximum of two nodes configured.

If the -a y or -a e option is executed on a currently active volume group, vgchange attempts to include any physical volumes that were previously listed as missing. This is useful if a physical volume has come back online. However, no automatic synchronization of any mirrored logical volumes is done. If synchronization is required, execute the vgsync command (see vgsync(1M)).

r

Activate each specified volume group and all associated physical and logical volumes for read-only access. This option is ignored for a volume group that is already activated.

If a volume group is marked as part of a high availability cluster, the high availability software must be running on the system; otherwise, the volume group is not activated.

n

Deactivate each specified volume group and its associated logical volumes. You must close the logical volumes prior to executing this option. For example, if the logical volume contains a file system, the file system must be unmounted.

-c cluster

Control the membership of volume groups in a high availability cluster. cluster can have one of the following values:

y: Mark each specified volume group as a member of the high availability cluster. The high availability software must be running; otherwise, the volume group is not marked. Needs to be done on one node only.
n: Remove each specified volume group from membership in the high availability cluster. The high availability software does not need to be running.

The volume group must be deactivated with the -a n option before a -c y|n option can be executed.

-S sharable

Control the sharability of volume groups in a high availability cluster. sharable can have one of the following values:

y: Mark each specified volume group as sharable. The high availability software must be running; otherwise, the volume group is not marked. Needs to be done on one node only.
n: Remove the shared attribute from the volume group. The high availability software does not need to be running.

The volume group must be deactivated with the -a n option before a -S y|n option can be executed.

-l

Disable the opening of logical volumes that belong to each specified volume group. If the -l option is set, later attempts to open the logical volumes will fail. To allow an opening of these logical volumes to succeed, execute lvchange -a y.

-p

Activate each specified volume group only if all of the physical volumes that belong to it are available.

-q quorum

Set the quorum enforcement for each specified volume group. quorum can have one of the following values:

y: Enforce the quorum requirement. This is the default.
n: Ignore the quorum requirement.

The -q n option can be used to activate the volume group when the disk quorum is not maintained because too many disks were lost. Since it ensures the integrity of the LVM configuration information, it is normally not advisable to override the quorum.

-s

Disable the synchronization of stale physical extents within the volume group specified by vg_name. This option is only effective when used with the -a y or -a e option.

-P resync_daemon_count

gives the advisory count to control the number of nomwcsyncd processes on volume group activation.

Mirrored Disk Activation

When the optional HP MirrorDisk/UX software is running and a volume group is activated, LVM performs the necessary mirror consistency recovery for each logical volume in the volume group based on the state of Mirror Write Cache and Mirror Consistency Recovery (see the Consistency Recovery section of lvdisplay(1M)). In a non-shared environment, LVM supports MWC, NOMWC and the NONE recovery. But in shared environment, LVM only supports NOMWC and the NONE recovery.

MWC: Recover mirror consistency by using the Mirror Write Cache and Mirror Consistency Record. This mode implies that the Mirror Write Cache is on.
NOMWC: Recover mirror consistency by searching all logical extents and copying data from a non-stale copy to the other mirror copies. This mode implies that the Mirror Write Cache is off.
NONE: Do not recover mirror consistency during volume group activation on this logical volume. This mode implies that the Mirror Write Cache is off.

Next, mirror synchronization refreshes stale mirror copies by copying data from a nonstale copy. If the -s option is specified on the command line, mirror synchronization does not occur. However, for those logical volumes that have Mirror Write Cache turned off, mirror synchronization is done independently of whether the -s option appears on the command line.

General Activation

If vgchange cannot access a physical volume, it lists the volume's status as missing. If too many physical volumes in the volume group are missing, vgchange reports that the group does not have a quorum and cannot be activated. The lack of a quorum can be overridden with the -q n option.

EXTERNAL INFLUENCES

Environment Variables

LANG determines the language in which messages are displayed.

If LANG is not specified or is null, it defaults to "C" (see lang(5)).

If any internationalization variable contains an invalid setting, all internationalization variables default to "C" (see environ(5)).

EXAMPLES

Activate volume group /dev/vg03:

vgchange -a y /dev/vg03 

Deactivate volume group /dev/vg03:

vgchange -a n /dev/vg03 

Activate volume group /dev/vg03 without synchronizing extents that are not current on logical volumes that have Mirror Write Cache turned on:

vgchange -a y -s /dev/vg03 

Exclusive Activation

Set up volume group /dev/vg03 for use in a high availability cluster:

vgchange -a n /dev/vg03   # Deactivate volume group
vgchange -c y /dev/vg03   # Enable volume group for HA cluster
vgchange -c y -S y /dev/vg03 # Enable volume group for HA cluster
                               and mark as sharable
vgchange -a e /dev/vg03   # Activate volume group in exclusive mode
vgchange -a s /dev/vg03   # Activate volume group in shared mode

Activate all volume groups; activate those that are marked for membership in a high availability cluster in exclusive mode:

vgchange -a y

Activate all volumes that are marked for membership in a high availability cluster in exclusive mode:

vgchange -a e

WARNINGS

Ordinary Operation

In ordinary operation (i.e., without the optional high availability software), it is possible to activate a volume group for read-write access from more than one physically connected system, leading to a high potential for data corruption. Therefore, if access is desired from more than one system to a single volume group, it is important that only one system activate the volume group for read-write access; the other systems can use read-only access. There is no problem if all systems activate the volume group for read-only access.

Furthermore, volume group information is only read from the disks during volume group activation. Dynamic changes to the volume group such as the following are not propagated to other systems sharing the volume group:

Logical volume configuration changes.
Changes to the status of the mirrored extents.
Bad-block relocation that occurs during write operations.

Because of these limitations, when sharing volume groups between systems it is recommended that logical volumes be accessed only by one system at a time. If logical volumes need to be accessed simultaneously, the logical volumes should not be mirrored and should not have bad-block relocation turned on, or all systems should use read-only access to the logical volumes.