Introduction: Hacks #58-67

While filesystem choices can have an effect on storage efficiency and performance, the hacks in this chapter address a variety of topics on getting the best raw hardware performance possible from your system board and disk drives. As with most performance-related things, lower timing values and higher clock, rotation, and data transfer speeds yield the best results.

Disk performance is ultimately measured in bytes transferred per second, which can be metered with a variety of benchmarking programs, such as SiSoft Sandra (http://www.sissoftware.net). Such programs can also tell you what the capabilities of your system board and disk drives are so you can determine if the real performance is living up to specification.

The following list describes the capabilities of each type of disk drive interface you're likely to encounter. From this list and a benchmarking program, you can tell what type of changes you can make to improve overall disk performance. Each version of the ATA specification, maintained by the industry trade group T13 (http://t13.org/), covers one or more implementations of technology and performance. You will find a lot of uses of the term ATA— UltraATA, UltraDMA, ATA-33, etc.—on product packages and advertising material. These labels may be misleading, as they can cover a wide range of capabilities from ATA-3 to ATA-5 rather than relating to specific industry standards. Check the product package and documentation to find the actual ATA industry standard a product is designed for when making performance comparisons. The current specification is ATA-5, which covers 44-133 Mbps data transfer rates using DMA-4 and UDMA-5 I/O methods.

ATA

Uses Programmed I/O Mode 1 (PIO-1) for a maximum data transfer rate of 4 megabytes per second (MBps). PIO mode requires constant attention by the CPU to handle data transfers at the expense of other I/O transactions and program operations.

ATA-2 (aka ATA-16)

Uses DMA-2 for a maximum data transfer rate of 16 MBps. DMA differs from PIO in that the CPU opens a direct memory-to-I/O device communications channel to let data flow freely without CPU intervention, so other I/O and program operations can continue at the same time.

ATA-3 (aka ATA-16)

Uses DMA-2 for a maximum data transfer rate of 16 MBps; ATA-3 devices are ATA-2 devices with the addition of S.M.A.R.T. internal drive diagnostic technology to "predict" drive failures.

ATA/ATAPI-4 (aka ATA-33, DMA-33, or UDMA-33)

Uses UDMA-2 for a maximum data transfer rate of 33 MBps.

ATA/ATAPI-5 (aka ATA-66, DMA-66, or UDMA-66)

This is the first in a series of devices with significant DMA-mode performance increases. Uses UDMA-4 for a maximum data transfer rate of 44 or 66 MBps. Requires 80-wire cable [Hack #59] to achieve maximum throughput.

ATA/ATAPI-5 (aka ATA-100 or UDMA-100)

This update to the ATA-5 specification increases the throughput capabilities to 100 Mbps using UDMA-5 I/O methods.

ATA/ATAPI-5 (aka ATA-133 or UDMA-133)

This update to the ATA-5 specification increases the throughput capabilities to 133 Mbps using UDMA-5 I/O methods.

As you can see from the list, Direct Memory Access (DMA) is required to achieve the highest possible performance, but data transfer mode is not the only determining factor affecting overall drive performance.

Direct Memory Access DMA is a feature that allows an I/O device and memory to directly interact for faster data transfer without the CPU. DMA transfers occur in a burst or periodic timeframe, allowing control to be returned to the CPU to handle other program operations.

There are three other factors about the hard drive itself to consider, rotation speed, seek time, and on-disk cache [Hack #58] .