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
