At 04:24 10/04/2005 +0000, Todd Walton wrote: >On 10/3/05, Gus Wirth <[EMAIL PROTECTED]> wrote: >> What makes you think that DMA isn't working? > >Gentoo: > >'hdparm /dev/hda' says: "using_dma = 0 (off)" and 'hdparm -d1 >/dev/hda' says: "HDIO_SET_DMA failed: Operation not permitted". >However... > >'hdparm -i /dev/hda' does have an asterisk next to "udma2". > >Knoppix: > >Same thing when I start up. 'hdparm' says DMA is off, 'hdparm -i' has >an asterisk next to udma2. However!, 'hdparm -d1' is able to turn DMA >on in Knoppix. > >So... one indication says it's on, one says not. And I'm not able to >turn it on.
It is already on. When you read out the settings of the hard drive using hdparm, you are reading what the drive actual has set. You can prove that DMA is on by doing a simple test. All you have to do is read or write a large block of data and see how long it takes. In a previous post I discussed testing data transfers between disks and the performance results. The numbers I came up with worked out to about 25MB/s sustained. However, for short bursts that fit within the buffer size of the hard drive, you will get a much higher rate, up to about the advertised rate for the controller/drive. Test this using the -t and -T parameter of hdparm. Read the man page for what these do. Then do a simple: # time dd if=/dev/hda of=/dev/null bs=4096 count=10000 Then use some simple math to figure out the data transfer rate. Gus -- [email protected] http://www.kernel-panic.org/cgi-bin/mailman/listinfo/kplug-list
