[GRLUG] External drive transfer rates

[Justin Denick]

On 11/5/07, Bob Kline <bob.kline at gmail.com> wrote:
>
>
>
> On Oct 22, 2007 11:05 AM, Justin Denick <justin.denick at gmail.com> wrote:
>
> >
> >
> >
> >
> > Be sure to see what  the DMA specs are too.
> >
> > hdparm -cuda /devx
> >
> > As you can see it makes a big differnece
> >
> > justin at da-boxx ~ $ sudo hdparm -t /dev/hda
> >
> > /dev/hda:
> >  Timing buffered disk reads:  166 MB in  3.02 seconds =  54.92 MB/sec
> > justin at da-boxx ~ $ sudo hdparm -d0 /dev/hda
> >
> > /dev/hda:
> >  setting using_dma to 0 (off)
> >  using_dma    =  0 (off)
> > justin at da-boxx ~ $ sudo hdparm -t /dev/hda
> >
> > /dev/hda:
> >  Timing buffered disk reads:   18 MB in  3.26 seconds =   5.53 MB/sec
> > justin at da-boxx ~ $ sudo hdparm -d1 /dev/hda
> >
> > /dev/hda:
> >  setting using_dma to 1 (on)
> >  using_dma    =  1 (on)
> > justin at da-boxx ~ $ sudo hdparm -t /dev/hda
> >
> > /dev/hda:
> >  Timing buffered disk reads:  166 MB in  3.02 seconds =  54.88 MB/sec
> > justin at da-boxx ~ $
> >
> > It's a kernel option
> > CONFIG_IDEDMA_AUTO=y
> >
> >
> >
> hdparm -cuda  /dev/x
>

I  forgot about one thing Bob.
hdparm only works for IDE drives, since your drive is interfaced via USB it
must be /dev/s-something right?

if that it the case than DMA shouldn't be needed at all.

As the purpose of DMA is to free up the processor maybe you should watch the
Load Avg when copying a file to see if it's
abnormally high.


only reports for a:  "readahead =  256 (on)
>
> Running   "hdparm -d1 /dev/x"
> result in "HDIO_SET_DEM failed: Invalid argument."
>
> The hdparm man page suggest that
> in rare cases one has to use the -X
> parameter.  It also says this can cause
> real headaches.
>
>     -Bob
>
>
>
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