Using hdparm - Intro

If you have an IDE hard disk that is less than a couple of years old and a controller to match, then most likely the manufacturers will boast about how quick the data transfer rates are.You may get near these figures on a windows system, but by default linux distributions will not use the fast PIO modes or any of the other setting to boost disk performance. The reason for this is due to the variety of hardware available each requiring different settings.

Before you proceed, please switch your box into single user mode (init 1) as specifing the wrong settings can cause data loss or for your machine to hang. Any commands listed below need to be ran as root.

Using hdparm - Getting Info

The first thing to do is find out what settings your drive supports, this is done by using the following command:

hdparm -i /dev/hdb

Settings are specified per drive so if you have more than one in your system it is best to one at a time. This gives us the all the information we need about the drive before any settings are changed:

/dev/hdb:

 Model=IBM-DJNA-352500, FwRev=J51OA30K, SerialNo=GW0GWF05809
 Config={ HardSect NotMFM HdSw>15uSec Fixed DTR>10Mbs }
 RawCHS=16383/16/63, TrkSize=0, SectSize=0, ECCbytes=34
 BuffType=3(DualPortCache), BuffSize=1966kB, MaxMultSect=16, MultSect=16
 DblWordIO=no, OldPIO=2, DMA=yes, OldDMA=2
 CurCHS=16383/16/63, CurSects=16514064, LBA=yes, LBAsects=49981680
 tDMA={min:120,rec:120}, DMA modes: mword0 mword1 mword2
 IORDY=on/off, tPIO={min:240,w/IORDY:120}, PIO modes: mode3 mode4
 UDMA modes: mode0 mode1 *mode2 mode3 mode4
 Drive Supports : ATA/ATAPI-4 T13 1153D revision 17 : ATA-1 ATA-2 ATA-3 ATA-4

Using hdparm - Speed Test

Before any of your drive's settings are changed a speed test should be done, so we can refer to it later to make sure that the drive's speed has been increased and we are not just wasting our time.
To do this hdparm can perform two benchmarks:

The speed of reading directly from the Linux buffer cache without disk access. (-t option)
The speed of reading through the buffer cache to the disk without any prior caching of data. (-T option)

The first shows us an indication of the throughput of the processor, cache, and memory of the system under test. The second measures how fast the drive can sustain sequential data reads, without any filesystem overhead.It is best to run these tests together as the second results are corrected for the first. It is also as usual to run these a couple of times to get accurate results. Here is the command you need to use:

hdparm -Tt /dev/hdb

You should some results similar to these below (results from PII 350Mhz with year old hard disk):

/dev/hdb:
 Timing buffer-cache reads:   128 MB in  1.25 seconds =102.40 MB/sec
 Timing buffered disk reads:  64 MB in 16.70 seconds =  3.83 MB/sec

Using hdparm - Settings explained

To list the current settings being used for your drive use the command:

hdparm /dev/hdb

This should produce the following output showingthe defualt (lowest) settings:

/dev/hdb:
 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     = 49585/16/63, sectors = 49981680, start = 0

Only the most supported options are listed below. Please view the man page for the more dangerous settings.

multcount (-m)
Permits the transfer of multiple sectors per I/O interrupt rather than the defualt of one. Check your "MaxMultSect" setting from your drive's information (above) to find the maximum value. A setting of 16 is a good value to try first, unless you have a Western Digital drive then should try a setting of 4 to 8.

I/O support (-c)
IDE 32-bit I/O support. One of the following numbers are used to enable/disable 32-bit I/O support:
0 to disable 32-bit I/O support
1 to enable 32-bit data transfers
3 to enable 32-bit data transfers with a special sync sequence
Note: IDE drives still have only a 16-bit connection over the ribbon cable from the interface card.

unmaskirq (-u)
Interrupt-unmask flag for the drive. A setting of 1 permits the driver to unmask other interrupts (eg. one from a network card) during processing of a disk interrupt, this show improve overall system response time.
Note: Use this feature with caution: some drives and controllers do not tolerate the increased I/O latencies possible when this feature is enabled, resulting in massive filesystem corruption.

using_dma (-d)
Disable/enable the Use of DMA operations for the drive. This option only works with a few combinations of drives and interfaces which support DMA and which are known to the IDE driver (eg. Intel's Triton chipset).
Best used with the "IDE transfer mode" option.

IDE transfer mode (-X)
This is used in combination with the "-d1" option to enable DMA for the drive. Two settings can be used here:
34 is used to select multiword DMA mode2 transfers
66 is used to select UltraDMA mode2 transfers (for systems which support UltraDMA burst timings)
68 is used to select UltraDMA mode4 transfers (for systems which support UltraDMA burst timings)
Note: An incorrect setting may cause your system to hang.

Using hdparm - Changing Settings

Changing the drive's settings is simple, you just specify each new setting in a row with spaces in between, followed by the drive as follows:

hdparm -X66 -d1 -u1 -m16 -c3 /dev/hdb

If your system locks up at this point then one of the setttings you changed is not supported, try only specifying one them one at a time to find the problem. After each setting change use hdparm's speed test to make sure that the drive's performance has improved. Here is the results of a speed test using the above settings:

/dev/hdb:
 Timing buffer-cache reads:   128 MB in  1.24 seconds =103.23 MB/sec
 Timing buffered disk reads:  64 MB in  4.31 seconds = 14.85 MB/sec

Once the new settings have been chosen and tested it's best to put this line in one of your start up files such as "boot.local", this file can reside in the directories below depending on which distribution you are using:

/etc/init.d/boot.local
/sbin/init.d/boot.local
/etc/rc.d/boot.local

These new settings should now be activated at every boot.