A quorum is the required number of physical volumes that must be available in a volume group to activate that volume group or for it to remain activated. To activate a volume group, more than half its disks that were available during the last activation must be online and in service. For the volume group to remain fully operational, at least half the disks must remain present and available.
During run time, when a volume group is already active, if a disk fails or is taken offline, the quorum might become lost. This condition occurs if less than half of the physical volumes defined for the volume group now remain fully operational. For example, if two disks belong to a volume group, the loss of one does not cause a loss of quorum as is the case when activating the volume group. To lose quorum, both disks must become unavailable. In that case, your volume group remains active, but a message prints to the console, indicating that the volume group has lost quorum. Until the quorum is restored (at least one of the LVM disks in the volume group in the previous example is again available), LVM does not allow you to complete most commands that affect the volume group configuration. Further, some of the I/O accesses to the logical volumes for that volume group might hang because the underlying disks are not accessible. Also, until quorum is restored, the MWC will not be updated because LVM cannot guarantee the consistency (integrity) of the LVM information.
Use the vgchange -q n option to override the system's quorum check when the volume group is activated. This option has no effect on the runtime quorum check. Overriding quorum can result in a volume group with an inaccurate configuration (for example, missing recently creating logical volumes). This configuration change might not be reversible.
root@syshpux:/hroot# ls -ld /dev/vg00
drwxr-xr-x 2 root root 8192 Apr 1 2009 /dev/vg00
root@syshpux:/hroot# ls -l /dev/vg00
total 0
crw-r----- 1 root sys 64 0x000000 Apr 1 2009 group
brw-r----- 1 root sys 64 0x000001 Apr 1 2009 lvol1
brw-r----- 1 root sys 64 0x00000a Apr 1 2009 lvol10
brw-r----- 1 root sys 64 0x00000b Apr 1 2009 lvol11
brw-r----- 1 root sys 64 0x00000c Apr 1 2009 lvol12
brw-r----- 1 root sys 64 0x00000d Apr 1 2009 lvol13
brw-r----- 1 root sys 64 0x000002 Apr 1 2009 lvol2
brw-r----- 1 root sys 64 0x000003 Apr 1 2009 lvol3
brw-r----- 1 root sys 64 0x000004 Apr 1 2009 lvol4
brw-r----- 1 root sys 64 0x000005 Apr 1 2009 lvol5
brw-r----- 1 root sys 64 0x000006 Apr 1 2009 lvol6
brw-r----- 1 root sys 64 0x000007 Apr 1 2009 lvol7
brw-r----- 1 root sys 64 0x000008 Apr 1 2009 lvol8
brw-r----- 1 root sys 64 0x000009 Apr 1 2009 lvol9
crw-r----- 1 root sys 64 0x000001 Apr 1 2009 rlvol1
crw-r----- 1 root sys 64 0x00000a Apr 1 2009 rlvol10
crw-r----- 1 root sys 64 0x00000b Apr 1 2009 rlvol11
crw-r----- 1 root sys 64 0x00000c Apr 1 2009 rlvol12
crw-r----- 1 root sys 64 0x00000d Apr 1 2009 rlvol13
crw-r----- 1 root sys 64 0x000002 Apr 1 2009 rlvol2
crw-r----- 1 root sys 64 0x000003 Apr 1 2009 rlvol3
crw-r----- 1 root sys 64 0x000004 Apr 1 2009 rlvol4
crw-r----- 1 root sys 64 0x000005 Apr 1 2009 rlvol5
crw-r----- 1 root sys 64 0x000006 Apr 1 2009 rlvol6
crw-r----- 1 root sys 64 0x000007 Apr 1 2009 rlvol7
crw-r----- 1 root sys 64 0x000008 Apr 1 2009 rlvol8
crw-r----- 1 root sys 64 0x000009 Apr 1 2009 rlvol9
root@syshpux:/hroot#
---------
class : lunpath, instance 10
Asynchronous write failed on LUN (dev=0x3000008)
IO details : blkno : 43177576, sector no : 87379152
LVM: WARNING: VG 64 0x000000: LV 9: Some I/O requests to this LV are waiting
indefinitely for an unavailable PV. These requests will be queued until
the PV becomes available (or a timeout is specified for the LV).
class : lunpath, instance 10
Asynchronous write failed on LUN (dev=0x3000008)
IO details : blkno : 23125536, sector no : 47275072
LVM: WARNING: VG 64 0x000000: LV 5: Some I/O requests to this LV are waiting
indefinitely for an unavailable PV. These requests will be queued until
the PV becomes available (or a timeout is specified for the LV).
class : lunpath, instance 10
Asynchronous write failed on LUN (dev=0x3000008)
IO details : blkno : 43177680, sector no : 87379360
class : lunpath, instance 4
Asynchronous write failed on LUN (dev=0x3000008)
IO details : blkno : 43223016, sector no : 87470032
LVM: WARNING: VG 64 0x000000: LV 13: Some I/O requests to this LV are waiting
indefinitely for an unavailable PV. These requests will be queued until
the PV becomes available (or a timeout is specified for the LV).
LVM: WARNING: VG 64 0x000000: LV 10: Some I/O requests to this LV are waiting
indefinitely for an unavailable PV. These requests will be queued until
the PV becomes available (or a timeout is specified for the LV).
LVM: VG 64 0x000000: Lost quorum.
This may block configuration changes and I/Os. In order to reestablish quorum at least 1 of the following PVs (represented by current link) must become available:
<3 0x000008>
LVM: VG 64 0x000000: PVLink 3 0x000008 Failed! The PV is not accessible.
LVM: WARNING: VG 64 0x000000: LV 4: Some I/O requests to this LV are waiting
indefinitely for an unavailable PV. These requests will be queued until
the PV becomes available (or a timeout is specified for the LV).
LVM: VG 64 0x000000: Reestablished quorum.
LVM: VG 64 0x000000: PVLink 3 0x000008 Recovered.
LVM: NOTICE: VG 64 0x000000: LV 5: All I/O requests to this LV that were
waiting indefinitely for an unavailable PV have now completed.
LVM: NOTICE: VG 64 0x000000: LV 4: All I/O requests to this LV that were
waiting indefinitely for an unavailable PV have now completed.
LVM: NOTICE: VG 64 0x000000: LV 13: All I/O requests to this LV that were
waiting indefinitely for an unavailable PV have now completed.
LVM: NOTICE: VG 64 0x000000: LV 10: All I/O requests to this LV that were
waiting indefinitely for an unavailable PV have now completed.
LVM: NOTICE: VG 64 0x000000: LV 9: All I/O requests to this LV that were
waiting indefinitely for an unavailable PV have now completed.
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