[mythtv-users] Recording issues with I/O load

[Ian Clark]

On 21 September 2011 09:51, Stefan Lands <e350notifier at alice.de> wrote:
> Hello,
>
> I'm trying to find help in solving an issue with my new mythtv-box. I've
> been using mythtv for a couple of years by now, but this time I'm having
> a problem which I cannot solve. I'm out of ideas.
>
[snip]
> - frontend.log contains errors like the following during playback,
> resulting from the corrupt data:
>
> 2011-09-19 14:43:45.334 [ac3 @ 0x8699960]frame sync error
> 2011-09-19 14:43:45.334 AFD Error: Unknown audio decoding error
> 2011-09-19 14:43:45.860 [ac3 @ 0x8699960]frame CRC mismatch
> 2011-09-19 14:43:45.860 [ac3 @ 0x8699960]frame sync error
> 2011-09-19 14:43:45.860 AFD Error: Unknown audio decoding error
> 2011-09-19 14:43:46.360 WriteAudio: buffer underrun
^-- This, and your description above do seem to suggest some kind of IO issue.

Are your HDs okay? Is your RAID okay, it's not running degraded is it?

Is your raid setup correctly (although I understand the issue of
misaligned blocks is not so great under linux as other systems?) as
incorrect setup can lead to a lot of reading (to calculate parity)
when doing writes although I'm assuming as this is full it's been
moved from a working system?

Can you post a copy of your boot dmesg?

What speeds do you see? If you run something like Bonnie++ on the raid
partition what kind of speeds do you see?

As a quick test, you could use DD.

cd to somewhere on the raid:

time dd if=/dev/zero of=atestfile ibs=1m count=100

This will write a 100M test file to the current directory. How long
does it take?

FYI it takes about 2/3 seconds on my box, that's writing to both a
regular HD and a RAID5 volume.

Do you have any spare HDs you can use? What happens if you put a
single SATA drive in instead of the RAID, does the problem remain?

What mode is your SATA controller in on the motherboard, ideally it
should be AHCI.

>
> Well, I'm out of ideas now what to try or change else. There's another
> system I built running fine in my family with the same Motherboard and
> the same software-configuration.

Does that system also have the software RAID5?

> The only difference is the DVB-setup
> consisting of  2x Mystique SaTiX DVB-S-PCI-cards (KNC-One clone).
> I know that the C-1500 in my system is rather old, but in the old
> AMD6000 it worked fine.
>
I'd be suprised if this was the issue for the reasons you say.

> I would be happy for suggestions which help me to find out what causes
> these problems. Or what can I do to dig deeper in my system to find the
> root of all evil.
>
> Thanks for your help.
>
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