Some root volume group terms are defined here:
- Mirroring provides redundant copies of AIX to prevent single points of
failure. AIX provides for the original copy of AIX, and one or two
additional copies. AIX places the data on the physical volumes in such
a way that no two copies of the same data are ever on the same physical
volume. This provides the redundancy necessary so that a single
physical volume failure does not cause its volume group to fail.
- A vote of the number of Volume Group Descriptor Areas (VGDAs) and Volume
Group Status Areas (VGSAs) that are active. For a volume group of one
disk, there are two VGDA/VGSAs. For a volume group of two disks, there
are two VGDA/VGSAs on the first disk and one on the second disk. For a
volume group of three or more disks, there is one VGDA/VGSA per disk.
A quorum ensures data integrity in the event of a disk failure. When
a majority (51 %) of the VGDA/VGSAs in the volume group cannot be accessed,
the group varies itself offline to prevent data loss or incorrect I/O
operations. An error log entry is produced when this situation
- A rule that AIX applies to the disks in a mirrored volume group.
The strictness rule requires that enough physical volumes with sufficient
space are part of a volume group, so that AIX can allocate the data according
to a particular algorithm. This algorithm allocates data among the
physical volumes in such a way that the loss of a single physical volume does
not constitute the loss of the volume group. Refer to the definition of
mirroring and unmirroring.
- Unmirroring reduces the number of copies of a root volume group.
For example, if there are currently three copies of the root volume group (the
original and two copies), unmirroring would be used to reduce the number of
copies from three to two or one. Optionally, physical volumes used for
mirroring may be removed from the root volume group after unmirroring.
When physical volumes are removed from the root volume group, they are made
available for use by other volume groups.
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