Tweaking hard disk on Linux

 
hdparm -Tt /dev/hda

/dev/hda:
Timing buffer-cache reads:   128 MB in  1.34 seconds =95.52 MB/sec
Timing buffered disk reads:  64 MB in 17.86 seconds = 3.58 MB/sec

hdparm /dev/hda

/dev/hda:
multcount    =  0 (off)
I/O support  =  0 (default 16-bit)
unmaskirq    =  0 (off)
using_dma    =  0 (off)
keepsettings =  0 (off)
nowerr       =  0 (off)
readonly     =  0 (off)
readahead    =  8 (on)
geometry     = 1870/255/63, sectors = 30043440, start = 0

1. multcount: Short for multiple sector count. This controls how many sectors are fetched from the disk in a single I/O interrupt. Almost all modern IDE drives support this. The man page claims: when this feature is enabled, it typically reduces operating system overhead for disk I/O by 30-50%. On many systems, it also provides increased data throughput of anywhere from 5% to 50%.
2. I/O support: This is a big one. This flag controls how data is passed from the PCI bus to the controller. Almost all modern controller chipsets support mode 3, or 32-bit mode w/sync. Some even support 32-bit async. Turning this on will almost certainly double your throughput (see below.)
3. unmaskirq: Turning this on will allow Linux to unmask other interrupts while processing a disk interrupt. What does that mean? It lets Linux attend to other interrupt-related tasks (i.e., network traffic) while waiting for your disk to return with the data it asked for. It should improve overall system response time, but be warned: Not all hardware configurations will be able to handle it. See the manpage.
4. using_dma: DMA can be a tricky business. If you can get your controller and drive using a DMA mode, do it. But I have seen more than one machine hang while playing with this option.

 
hdparm -X66 -d1 -u1 -m16 -c3 /dev/hda:
setting 32-bit I/O support flag to 3
setting multcount to 16
setting unmaskirq to 1 (on)
setting using_dma to 1 (on)
setting xfermode to 66 (UltraDMA mode2)
multcount    = 16 (on)
I/O support  =  3 (32-bit w/sync)
unmaskirq    =  1 (on)
using_dma    =  1 (on)

hdparm -tT /dev/hda

/dev/hda:
Timing buffer-cache reads:   128 MB in  1.43 seconds = 89.51 MB/sec
Timing buffered disk reads:  64 MB in  3.18 seconds = 20.13 MB/sec