[mythtv-users] Disk I/O problems?

[Karl Newman]

On Fri, Aug 22, 2014 at 1:52 PM, Stephen Worthington <
stephen_agent at jsw.gen.nz> wrote:

> On Sat, 23 Aug 2014 02:46:10 +1000, you wrote:
>
> >Since upgrading to 0.27.3 I've been having bad problems with playback
> stutter
> >and failures.
> >
> >
> >hdparm on my disks seem somewhat slow:
> >
> >sudo hdparm -tT /dev/sda
> >
> >/dev/sda:
> > Timing cached reads:   2134 MB in  2.00 seconds = 1067.96 MB/sec
> > Timing buffered disk reads: 232 MB in  3.01 seconds =  77.01 MB/sec
> >
> >Is this normal for WD 1TB Greens? unfortunately I don't know what they
> were in
> >the past :)
> >
> >
> >thanks,
>
> Check your logs to see if the drive is running SATA 1 (1.5 Gbit/s)
> instead of 3 or 6 Gbit/s.  Sometimes I have seen drives and
> controllers just fail to negotiate properly and drop to the lower
> speed.  If you have that sort of problem, check the cable and try a
> cold reboot (power off for at least 60 seconds before rebooting).
>

I had a problem with my drives--they dropped to ATA or whatever sort of
compatibility mode when I replaced the motherboard (and every time I
upgraded the BIOS), which means I lost NCQ. NCQ appears to give me a big
performance boost or at least seems to allow heavy concurrent access
without causing playback or recording to stutter. Without it, I would have
to ionice any operation that would take more than a couple seconds like
copying large files. You can check if your drives are NCQ capable with the
command 'dmesg | grep NCQ' You're looking for something like 'NCQ (depth
31/32)' Something other than 0/32 anyway. See this post for details:
http://exemen.wordpress.com/2011/05/16/enabling-disabling-and-checking-ncq/
The solution in my case was just to go into the BIOS and make sure the
controllers were set for AHCI mode.

Sincerely,

Karl
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