[GRLUG] External drive transfer rates

[Bob Kline]

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

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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