PC Hacks 100 Industrial-Strength Tips and Tools

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Hack 67 Linux's Drive Performance Booster

To be on the safe side, your new Linux installation starts up with the least common denominator of disk drive performance capabilities—typically DMA-33—robbing you of 50-150% of your potential performance. Once Linux is installed, you are free and encouraged to start tweaking the configuration of your disk drive and its interface to squeeze the most of them.

Setting HDPARM parameters too aggressively—that is, in excess of the disk controller or drive capabilities—can lead to data loss. It is best to test HDPARM settings on a fresh installation of the operating system before committing any applications or programs to the drive and prepare to back down on the settings and reinstall the OS if the drive is unstable or the HDPARM tests show erratic results or fail.

The tool needed, HDPARM, is included with the operating system (or available from your package manager). It can be adjusted manually and then put into a startup script to make your chosen settings effective every time the system starts up.

HDPARM is a command-line utility that provides powerful control over your hard drive parameters (HD PARaMeters). It can also tell you a lot about your disk drive. Everything you do with HDPARM, until you make a script for it, will be done at the command line.

You must be logged in as root to run HDPARM. You can also use the sudo command to run the command as root if you have sufficient privileges.

Assume /dev/hda is the designation for your hard drive. (This is the default for the first IDE drive; a SATA drive may appear as /dev/hde if your motherboard also has IDE interfaces.) Run the following command:

hdparm -i /dev/hda

You should get some info like the following:

/dev/hda:

Model=QUANTUM FIREBALLlct, FwRev=APL.1234, SerialNo=1234567

Config={ HardSect NotMFM HdSw>15uSec Fixed DTR>10Mbs } 

RawCHS=16383/16/63, TrkSize=32256, SectSize=21298, ECCbytes=4 

BuffType=DualPortCache, BuffSize=418kB, MaxMultSect=8, MultSect=off

CurCHS=16383/16/63, CurSects=-66060037, LBA=yes, LBAsects=39876478

IORDY=on/off, tPIO={min:120,w/IORDY:120}, tDMA={min:120,rec:120} 

PIO modes: pio0 pio1 pio2 pio3 pio4 

DMA modes: mdma0 mdma1 mdma2 udma0 udma1 udma2 udma3 udma4 *udma5 

AdvancedPM=no 

Drive Supports : ATA/ATAPI-5 T13 1321D revision 1 : ATA-1 ATA-2 

ATA-3 ATA-4 ATA-5

This tremendous amount of data provided tells you:

MaxMultSect

The maximum number of sectors your hard disk can read at a time.

MultSect

The current number of sectors being read at a time.

PIO modes and DMA modes

The modes supported by your hard drive. The one marked with an asterisk (*) is the one currently set.

AdvancedPM

Indicates whether or not your hard drive supports Advanced Power Management.

Another command:

hdparm /dev/hda

reveals the following information:

/dev/hda: 

multcount = 0 (on) 

I/O support = 0 (16-bit) 

unmaskirq = 0 (off) 

using_dma = 0 (off) 

keepsettings = 0 (off) 

nowerr = 0 (off) 

readonly = 0 (off) 

readahead = 8 (on) 

geometry = 2482/255/63, sectors = 39876480, start = 0

The items of interest are:

multcount

The number of sectors being read at a time.

I/O support

The operating mode of your hard disk (16/32/32sync).

using_dma

Whether or not the drive is using the DMA feature. This may be on by default if your version of Linux properly detects and supports your chipset and drive's DMA capabilities.

keepsettings

Whether the settings are kept after the drive resets (usually caused by errors).

readonly

Whether the drive is read-only. Normally set to 1 only for CD-ROMs.

readahead

How many sectors ahead will be read when you access the hard drive.

The HDPARM program provides two performance-testing features that are crucial to letting you know whether or not you're making improvements as you tweak along. The command:

hdparm -Tt /dev/hda1

will show results such as the following before enhancing the performance:

/dev/hda1:

Timing buffer-cache reads: 128 MB in 5.97 seconds = 21.43 MB/sec

Timing buffered disk reads: 64 MB in 17.97 seconds = 3.56 MB/sec

and then results like these after enhancing the performance:

Timing buffer-cache reads: 128 MB in 0.91 seconds =140.66 MB/sec

Timing buffered disk reads: 64 MB in 3.78 seconds = 16.93 MB/sec

The goal of this hack is to see the time in seconds decrease and the MB/sec to increase. You can do that by using a variety of parameters, invoked one at a time, then rerunning the performance tests to see if things are improving or not.

Mistakes during the setup process may damage your filesystem and all of its data, so it's best to do this after a fresh install of Linux or right after you've done a full backup.

Begin by setting the operating mode of the interface between the system and the disk drive using one of the following parameters:

hdparm -c0 /dev/hda  #sets operating mode to 16-bits

hdparm -c1 /dev/hda  #sets operating mode to 32-bits

hdparm -c3 /dev/hda  #sets operating mode to 32-bits synchronized

Mode 1 (-c1) is used most often for best performance. Mode 3 (-c3) only is needed for some chipsets.

Next set the data transfer parameters, which you can determine from the output of the "-I" command shown earlier (in that case 8 is the maximum supported):

hdparm -m8 /dev/hda

Next try activating DMA mode for your system interface:

hdparm -d1

Then set the drive mode (a value of X32 is most common; UDMA-5 is X69):

hdparm -X32 /dev/hda

or:

hdparm -X69 /dev/hda

Finally, try setting the read-ahead value, which is typically set to the same value as multcount from earlier, or 8:

hdparm -a8 /dev/hda

If any or all of these settings make incremental improvements in performance, remember them and create a script that sets them all sequentially or includes them all in one line. I prefer sequential lines to ensure the drive accepts each command separately and I do not lose a setting if another fails to take. From all of this, you might typically be using the following parameters:

hdparm -c1

hdparm -m8 /dev/hda

hdparm -d1

hdparm -X34 /dev/hda

hdparm -a8 /dev/hda

Another single-command example that may work best for your system is:

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

Save either to a file and make the file a script to place in the directory for the runlevel at which you normally use Linux. For example:

The rc5.d part of the parameter string indicates runlevel 5, which is the normal operating mode for most Linux systems. To find out your default runlevel, examine /etc/inittab for the inittdefault entry, as in:

id:5:initdefault:

The next step is to keep an eye on dmesg and/or /var/log/syslog. In some cases, an error will cause the settings to be reset. So that's where the -k (keep) flag comes in. If you're 100% positive that these settings won't corrupt your data, you can add -k to the script.

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