Speeding up Linux Using hdparm

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Speeding up Linux Using hdparm
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Turbocharged

So, since we have our system in single-user mode like a good little admin, let's try out some turbo settings:

hdparm -c3 -m16 /dev/hda

/dev/hda:
 setting 32-bit I/O support flag to 3
 setting multcount to 16
 multcount    =  16 (on)
 I/O support  =  3 (32-bit w/sync)

Great! 32-bit sounds nice. And some multi-reads might work. Let's re-run the benchmark:

hdparm -tT /dev/hda


/dev/hda:
 Timing buffer-cache reads:   128 MB in  1.41 seconds =90.78 MB/sec
 Timing buffered disk reads:  64 MB in  9.84 seconds = 6.50 MB/sec

WOW! Almost double the disk throughput without really trying! Incredible.

But wait, there's more: We're still not unmasking interrupts, using DMA, or even a using decent PIO mode! Of course, enabling these gets riskier. (Why is it always a trade-off between freedom and security?) The man page mentions trying Multiword DMA mode2, so:

hdparm -X34 -d1 -u1 /dev/hda

...Unfortunately this seems to be unsupported on this particular box (it hung like an NT box running a Java app.) So, after rebooting it (again in single-user mode), I went with this:

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

/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)

And then checked:

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

20.13 MB/sec. A far cry from the miniscule 3.58 we started with...

By the way, notice how we specified the -m16 and -c3 switch again? That's because it doesn't remember your hdparm settings between reboots. Be sure to add the above line (not the test line with -tT flags!) to your /etc/rc.d/* scripts once you're sure the system is stable (and preferably after your fsck runs; having an extensive fs check run with your controller in a flaky mode may be a good way to generate vast quantities of entropy, but it's no way to administer a system. At least not with a straight face...)

Now, after running the benchmark a few more times, reboot in multi-user mode and fire up X. Load Netscape. And try not to fall out of your chair.

In conclusion

This is one of those interesting little tidbits that escapes many "seasoned" Linux veterans, especially since one never sees any indication that the system isn't using the most optimal settings. (Gee, all my kernel messages have looked fine....) And using hdparm isn't completely without risk, but is well worth investigating.

And it doesn't stop at performance: hdparm lets you adjust various power saving modes as well. See the hdparm(8) for the final word.

Many thanks to Mark Lord for putting together this nifty utility. If your particular distribution doesn't include hdparm (usually in /sbin or /usr/sbin), get it from the source at http://metalab.unc.edu/pub/Linux/system/hardware/

Happy hacking!

Rob Flickenger is a long time supporter of FreeNetworks and DIY networking. Rob is the author of three O'Reilly books: Building Wireless Community Networks, Linux Server Hacks, and Wireless Hacks.

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