Position on physical volume

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The Intra-Physical Volume Allocation Policy specifies what strategy should be used for choosing physical partitions on a physical volume. The five general strategies are edge, inner-edge, middle, inner-middle, and center.

Figure 1. Intra-Physical Volume Allocation Policy. This figure illustrates storage position on a physical volume or disk. The disk is formatted into hundreds of tracks beginning at the outer edge of the disk and moving toward the center of the disk. Because of the way a disk is read (the tracks spinning under a movable read/write head), data that is written toward the center of the disk will have faster seek times than data that is written on the outer edge. In part, this is due to the mechanical action of the read/write head and the sectors of each track having to pass under the head. Data is more dense as it moves toward the center, resulting in less physical movement of the head. This results in faster overall throughput.
Intra-Physical Volume Allocation Policy

Physical partitions are numbered consecutively, starting with number one, from the outer-most edge to the inner-most edge.

The edge and inner-edge strategies specify allocation of partitions to the edges of the physical volume. These partitions have the slowest average seek times, which generally result in longer response times for any application that uses them. Edge on disks produced since the mid-1990s can hold more sectors per track so that the edge is faster for sequential I/O.

The middle and inner-middle strategies specify to avoid the edges of the physical volume and out of the center when allocating partitions. These strategies allocate reasonably good locations for partitions with reasonably good average seek times. Most of the partitions on a physical volume are available for allocation using this strategy.

The center strategy specifies allocation of partitions to the center section of each physical volume. These partitions have the fastest average seek times, which generally result in the best response time for any application that uses them. Fewer partitions on a physical volume satisfy the center strategy than any other general strategy.

The paging space logical volume is a good candidate for allocation at the center of a physical volume if there is lot of paging activity. At the other extreme, the dump and boot logical volumes are used infrequently and, therefore, should be allocated at the beginning or end of the physical volume.

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