[mythtv-users] MySQL on SSD 99% Utilization

[Brian Long]

On Thu, Feb 3, 2011 at 2:44 PM, Eric Sharkey <eric at lisaneric.org> wrote:

> On Thu, Feb 3, 2011 at 11:40 AM, Brian Long <briandlong at gmail.com> wrote:
> > Is it generally a
> > bad practice to put MySQL on a SSD?  I figured it would provide a nice
> fast
> > DB and keep my DB separate from my recording disks, but I guess I was
> wrong.
>
> I have my backend's MySQL db on an SSD, with the recordings on a
> magnetic disk, and I don't have anything like the problems you're
> seeing.  Moving the db to the SSD seems to have been a big boost to
> responsiveness when it comes to searching/scheduling new recordings or
> bringing up the guide data.
>
> One thing I have noticed with iostat is that it tends to report
> elevated numbers on its first invocation, which is why I always give
> it a repeat interval (usually 2 seconds) and watch until it appears to
> be at a steady state.
>
> I have comm flagging going on right now and here's what I see
> (/dev/sda is my SSD):
> <snip>
> So I think something is seriously misconfigured on your system.
>

Yes, I didn't dig deep enough and it's not MySQL slamming my SSD; it's the
mythbackend logging to /var/log which is also on my SSD.  I tried tuning
MySQL and moving /var/lib/mysql to spinning disk and noticed the SSD was
still 99% utilized.  Then I noticed my mythcommflag job was endlessly
logging the following types of errors:
2011-02-03 15:10:43.547 AFD Error: Unknown decoding error
2011-02-03 15:10:43.564 [h264 @ 0x37412f7ec0]decode_slice_header error
2011-02-03 15:10:43.583 [h264 @ 0x37412f7ec0]no frame!
2011-02-03 15:10:43.583 [h264 @ 0x37412f7ec0]get_buffer() failed (stride
changed)
2011-02-03 15:10:43.604 [h264 @ 0x37412f7ec0]decode_slice_header error
2011-02-03 15:10:43.653 [h264 @ 0x37412f7ec0]no frame!

Mythbackend seems to be DOS'ing my SSD!  :-)  I guess I need to dig into
removing that job from the queue since mythcommflag doesn't like the
recording.

/Brian/
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