Disk reads from mirror chunks

The database server uses mirroring to improve read performance because two versions of the data are located on separate disks. A data page is read from either the primary chunk or the mirror chunk, depending on which half of the chunk includes the address of the data page. This feature is called a split read. Split reads improve performance by reducing the disk-seek time. Disk-seek time is reduced because the maximum distance over which the disk head must travel is reduced by half. The following figure illustrates a split read.
Figure 1. Split read reducing the maximum distance over which the disk head must travel
This figure shows that the database server reads data from half of the primary chunk and half of the mirror chunk.

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