Intra-disk allocation policies for each logical volume

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The intra-disk allocation policy choices are based on the five regions of a disk where physical partitions can be located.

The closer a given physical partition is to the center of a physical volume, the lower the average seek time is because the center has the shortest average seek distance from any other part of the disk.

The file system log is a good candidate for allocation at the center of a physical volume because it is so frequently used by the operating system. At the other extreme, the boot logical volume is used infrequently and therefore is allocated at the edge or middle of the physical volume.

The general rule is that the more I/Os, either absolutely or during the running of an important application, the closer to the center of the physical volumes the physical partitions of the logical volume needs to be allocated.

This rule has one important exception: Mirrored logical volumes with Mirror Write Consistency (MWC) set to On are at the outer edge because that is where the system writes MWC data. If mirroring is not in effect, MWC does not apply and does not affect performance.

The five regions where physical partitions can be located are as follows:
  1. outer edge
  2. inner edge
  3. outer middle
  4. inner middle
  5. center
The edge partitions have the slowest average seek times, which generally result in longer response times for any application that uses them. The center partitions have the fastest average seek times, which generally result in the best response time for any application that uses them. There are, however, fewer partitions on a physical volume at the center than at the other regions.