Section 4.4. Sector Zoning

4.4. Sector Zoning

Sector zoning, also known as Multiple Zone Recording (MZR), is a disk layout strategy for optimal performance. A track on the outside edge of a disk can contain more sectors than one on the inside because a track on the outside edge has a greater length. Since the disk can read more sectors per rotation from the outside edge than the inside, data stored near the outside edge is faster. Manufacturers often break disks into zones of fixed sector per-track ratios, with the number of zones and ratios chosen for both performance and data density.

Data throughput on the outside edge may also be faster because many disk heads rest at the outside edge, resulting in reduced seek times for data blocks nearby.

A simple way to demonstrate the effect of sector zoning is to perform a sequential read across the entire disk. The following example shows the throughput at the start of the test (outside edge) and at the end of the test (inside edge).

# dd if=/dev/rdsk/c0t0d0s2 of=/dev/null bs=128k $ iostat -xnz 10 ...                     extended device statistics     r/s    w/s   kr/s   kw/s wait actv wsvc_t asvc_t  %w  %b device   104.0    0.0 13311.0    0.0  0.0  1.0    0.0    9.5   0  99 c0t0d0 ...                     extended device statistics     r/s    w/s   kr/s   kw/s wait actv wsvc_t asvc_t  %w  %b device    71.1    0.0 9100.4    0.0  0.0  1.0    0.0   13.9   0  99 c0t0d0 

Near the outside edge the speed was around 13 Mbytes/sec, while at the inside edge this has dropped to 9 Mbytes/sec. A common procedure that takes advantage of this behavior is to slice disks so that the most commonly accessed data is positioned near the outside edge.