adeffs.mythtv at gmail
Sep 28, 2006, 6:55 AM
Post #4 of 4
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On 9/27/06, Robin Hill <myth [at] robinhill> wrote:
> On Wed Sep 27, 2006 at 02:42:33PM -0500, Allan Wilson wrote:
> > I have a PIV 3.0 GHz system for my backend that has a hard time plalying
> > back HD content especially when other things are going on. I know this is
> > the low end of what it takes to run HD using the processor but reading some
> > older posts I came back to the subject of dma and sata support for that
> > feature in the linux kernel. Can you set dma on a sata device? What kind of
> > speeds should I be getting out of my sata drives? I have the Intel ICH5
> > chipset. Running the following commands I get:
> >
> > sudo hdparm -d1 /dev/sda
> > /dev/sda:
> > settign using_dma to 1 (on)
> > HDIO_SET_DMA failed: Inappropriate ioctl for device
> >
> You don't need to enable DMA for SATA drives. Since all SATA drives
> have DMA, and all SATA controllers support it, it's enabled by default.
> I also don't think hdparm works at all with SATA drives - IIRC you
> should be using sdparm (as they're seen using a SCSI style driver).
>
> > and for a speed test I got:
> >
> > sudo hdparm -tT /dev/sda
> > /dev/sda:
> > Timing cached reads: 2604 MB in 2.00 seconds = 1300.90 MB/sec
> > Timing buffered disk reads: 176 MB in 3.02 seconds = 58.29 MB/sec
> > /dev/sdb:
> > Timing cached reads: 2576 MB in 2.00 seconds = 1287.55 MB/sec
> > Timing buffered disk reads: 180 MB in 3.01 seconds = 59.85 MB/sec
> > /dev/sdc:
> > Timing cached reads: 2588 MB in 2.00 seconds = 1293.55 MB/sec
> > Timing buffered disk reads: 190 MB in 3.02 seconds = 62.99 MB/sec
> >
> > This speed is pretty constant and I wasn't really doing anything on the hard
> > drive when I ran the tests.
> >
>
> There certainly doesn't look to be anything wrong with these speeds. I
> don't see these affecting system performance at all (of course, it
> depends on how many processes are accessing the disks simultaneously).
if you want to see if disk i/o may be affecting your playback, run top
via ssh and look at the %wa value, which from what i understand is
basically the wait time on disk i/o, so the higher the percentage the
more data is being waited for (or something like that...)
--
Steve
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