Inter-disk settings for logical volume copies

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The allocation of a single copy of a logical volume on disk is fairly straightforward.

When you create mirrored copies, however, the resulting allocation is somewhat complex. The figures that follow show minimum maximum and inter-disk (Range) settings for the first instance of a logical volume, along with the available Strict settings for the mirrored logical volume copies.

For example, if there are mirrored copies of the logical volume, the minimum setting causes the physical partitions containing the first instance of the logical volume to be allocated on a single physical volume, if possible. Then, depending on the setting of the Strict option, the additional copy or copies are allocated on the same or on separate physical volumes. In other words, the algorithm uses the minimum number of physical volumes possible, within the constraints imposed by other parameters such as the Strict option, to hold all the physical partitions.

The setting Strict = y means that each copy of the logical partition is placed on a different physical volume. The setting Strict = n means that the copies are not restricted to different physical volumes. By comparison, the Super Strict option would not allow any physical partition from one mirror to be on the same disk as a physical partition from another mirror of the same logical volume.

Note: If there are fewer physical volumes in the volume group than the number of copies per logical partition you have chosen, set Strict to n. If Strict is set to y, an error message is returned when you try to create the logical volume.

The following figure illustrates a minimum inter-disk allocation policy with differing Strict settings:

Figure 1. Minimum Inter-Disk Policy/Strict. This illustration shows that if the Strict option is equal to Yes, each copy of the logical partition is on a different physical volume. If Strict is equal to No, all copies of the logical partitions are on a single physical volume.

The following figure illustrates a maximum inter-disk allocation policy with differing Strict settings:

Figure 2. Maximum Inter-Disk Policy/Strict. This illustration shows that if the Strict option is equal to Yes, each copy of a partition is on a separate physical volume. If Strict is equal to No, all copies are on a single physical volume.