enabling DMA on hard drives

[Matt Cahill]

Wednesday, January 19, 2005, 4:30:31 AM, you wrote:
PLP> On Tue, 18 Jan 2005, Lennart Sorensen wrote:

>> The kernel MIGHT enable DMA by default, but then again it might be
>> configured not to.  Without DMA most systems I have seen give about 2 or
>> 3MB/s transfer rate, while with DMA they give anywhere from 10 to 60MB/s
>> (as per hdparm -t measurements).  The hdparm -T measurement seems to be
>> a linux memory cache benchmark, which depends entirely on the cpu and
>> memory subsystem of the machine and has nothing to do with the actual
>> disk or controller.  DMA of course also significantly reduces the cpu
>> load required to operate the disk.

PLP> The kernel always uses the default mode of the drive, and won't 'tune'
PLP> anything it is not asked to. dma is enabled by scripts in init.d etc.


  Actually, if you look at the link I originally posted, there's an
  app by the name of hwtools, which can be set to enable the 'hdparm'
  command during boot-up.

  So, for example, the author has the following lines in
  '/etc/init.d/hwtools':

hdparm -d1 -X69 -m1 -c3 /dev/hda
hdparm -d1 /dev/hd[cd]

  I realise there's some debate here about the efficacy of hdparm in the
  grand scheme of things, but, superficially, I can say that my
  post-tweak results of 'hdparm -t /dev/hda' show a marked increase in
  the Mb/sec rate.

  Matt


-- 

Matt Cahill
                      m dash cahill at rogers dot com


"It is important to have this idea in one's mind, because otherwise
 one fails to grasp the whole spirit of modern Science-Philosophy.
 It does not aim at Truth; [...] it aims at maximum convenience."
 - A. Crowley

--
The Toronto Linux Users Group.      Meetings: http://tlug.ss.org
TLUG requests: Linux topics, No HTML, wrap text below 80 columns
How to UNSUBSCRIBE: http://tlug.ss.org/subscribe.shtml