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Diagnosis Guide

Root Volume Group terminology

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 occurs.

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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