HP-UX Reference (11i v3 07/02) - 1M System Administration Commands N-Z (vol 4)

p
pvchange(1M) pvchange(1M)
extents from a spare physical volume will be available as part of the "free" pool of
extents in the volume group. A spare physical volume will only be used in the
event that another physical volume within this volume group becomes unavail-
able (fails). sparepv can have one of the following values:
y Change the specified physical volume to be a "stand-by" spare for its volume
group. The specified physical volume must not have extents allocated on it
(i.e., no logical volumes residing on it) at the time this command is issued.
A stand-by spare physical volume will only be used in the event of a failure
of another physical volume -- prior to such a failure, no logical volume is
allowed to reside on it.
n Change the specified spare physical volume back into a regular physical
volume. If the physical volume was a stand-by spare, then all of the disk
space associated with it will be immediately available for use by logical
volumes. If the physical volume is an "active" spare, that is, it was previ-
ously a stand-by spare but then took over for a failed physical volume, it
will simply mark the physical volume as a regular member of its volume
group and the logical volumes residing on it will remain unchanged.
Attaching and Detaching Physical Volumes
Detaching a physical volume makes the data on that disk unavailable. LVM will not write or read any user
data or LVM metadata to the disk while it is detached. Consequently, it is important for the administrator
to ensure that the data on the disk is sufficiently mirrored to satisfy availability requirements prior to mak-
ing the device unavailable by detaching it.
Although detaching a path or physical volume ensures it is unavailable to LVM, attaching a path or physi-
cal volume will not necessarily make the path or physical volume available again. Attaching a path or phy-
sical volume only makes it available for LVM to use once the disk is working. For instance, if a disk is spin-
ning up, LVM will successfully attach the disk, but the disk will not be available until it is ready.
Detaching a physical volume or path only temporarily changes the status of the indicated path or physical
volume. However, it does not change the volume group configuration. When a physical volume is detached,
it will automatically be attached again the next time the volume group is activated using the
vgchange
command (see vgchange(1M)). If the objective is to permanently add or remove a path or physical volume
from the volume group, the vgextend or vgreduce commands (see vgextend(1M), and vgreduce(1M))
should instead be used.
Warning: Detaching any physical volume or path using the
-a N
or -a n options also disables automati-
cally attaching any paths to any of the physical volumes in the volume group. LVM will no longer attempt
to automatically recover any unattached physical volumes in the volume group, not just the ones explicitly
detached. To cause LVM to once again automatically attach devices in the volume group use the
-a y
options of vgchange command.
Attaching or Detaching Physical Volumes in Shared Volume Groups
The scope of the pvchange command is limited to the specific node on which it runs. Systems that are
part of a Serviceguard cluster operate independently. To replace disks that are part of a volume group
shared by a Serviceguard cluster, the physical volume must be detached and attached independently on
each of the systems in the cluster.
Alternate Links (PVLINKS)
In this release of HP-UX, LVM continues to support Alternate Links to a device to allow continued access to
the device, if the primary link fails. This multiple link or multipath solution increases data availability, but
does not allow the multiple paths to be used simultaneously.
There is a new feature introduced in the Mass Storage Subsystem on this version of HP-UX that also sup-
ports multiple paths to a device and allows access to the multiple paths simultaneously. The Mass Storage
Subsystem will balance the I/O load across the valid paths. This new multi-path behavior is enabled and
disabled through the use of the scsimgr command. See scsimgr(1M) for details.
It is no longer required or recommended to configure LVM with alternate links. However, it is possible to
maintain the traditional LVM behavior. To do so, both of the following criteria must be met:
• Only the legacy device special file naming convention is used in the volume group configuration.
• The scsimgr command is used to disable the Mass Storage Subsystem multipath behavior.
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