[mythtv-users] SATA drive speeds

[Steven Adeff]

On 9/27/06, Robin Hill <myth at robinhill.me.uk> 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
Before you ask, read the FAQ!
http://www.mythtv.org/wiki/index.php/Frequently_Asked_Questions
then search the Wiki, and this list,
http://www.gossamer-threads.com/lists/mythtv/
Mailinglist etiquette -
http://www.mythtv.org/wiki/index.php/Mailing_List_etiquette