Range of physical volumes

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The Inter-Physical Volume Allocation Policy specifies which strategy should be used for choosing physical devices to allocate the physical partitions of a logical volume. The choices are the minimum and maximum options.

Figure 1. Inter-Physical Volume Allocation Policy. This illustration shows 2 physical volumes. One contains partition 1 and a copy of partition 2. The other contains partition 2 with a copy of partition 1. The formula for allocation is Maximum Inter-Disk Policy (Range=maximum) with a Single Logical Volume Copy per Disk (Strict=y).
Inter-Physical Volume Allocation Policy

The minimum option indicates the number of physical volumes used to allocate the required physical partitions. This is generally the policy to use to provide the greatest reliability and availability, without having copies, to a logical volume. Two choices are available when using the minimum option, with copies and without, as follows:

  • Without Copies: The minimum option indicates one physical volume should contain all the physical partitions of this logical volume. If the allocation program must use two or more physical volumes, it uses the minimum number possible, remaining consistent with the other parameters.
  • With Copies: The minimum option indicates that as many physical volumes as there are copies should be used. If the allocation program must use two or more physical volumes, the minimum number of physical volumes possible are used to hold all the physical partitions. At all times, the constraints imposed by other parameters such as the strict option are observed.

These definitions are applicable when extending or copying an existing logical volume. The existing allocation is counted to determine the number of physical volumes to use in the minimum with copies case, for example.

The maximum option indicates the number of physical volumes used to allocate the required physical partitions. The maximum option intends, considering other constraints, to spread the physical partitions of this logical volume over as many physical volumes as possible. This is a performance-oriented option and should be used with copies to improve availability. If an uncopied logical volume is spread across multiple physical volumes, the loss of any physical volume containing a physical partition from that logical volume is enough to cause the logical volume to be incomplete.