[techtalk] hdparm and DMA "not permitted"

[James Sutherland]

On Wed, 23 May 2001, Penguina wrote:

> WOW THANKS!
>
> I just recompiled my 2.4.0 kernel with generic dma support
> for the IDE driver on my laptop, and it more than quadrupled my
> disk reads.  (We'll see how it handles disk *writes* from my DV
> camera now...)

One other point you may wish to check, BTW, is what transfer mode you're
using. This is set using the -X switch with hdparm; for UDMA mode X, you
want 64+X. I can get UDMA mode 5 on my Fujitsu drives (i.e. -X 69), but
some drives won't make it this high.

For "Multiword DMA", use 32+X instead.
For PIO (the worst mode) use 0.

hdparm -Tt can be a good rough indicator of how well your disk performs
with each setting, BTW - it only takes a couple of seconds to give an
indication of read speed.


James.