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

[Stefan Lands]

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.

My last mythtv-box used to be a AMD6000+ powered system, which ran fine
over the years. But in the meantime the electrical-bills got higher from
year to year, so I thought of building a new system, which takes much
less energy to run 24/7. So I bought pretty new hardware:

- ASUS E35 M1-M Pro with 4GB RAM
- 1x SATA-HDD (which contains Ubuntu 10.04 as well as the
mythtv-recording-directories)
- 3x SATA-HDD (SW-RAID5 containing many archived recordings I wanna keep)
- 1x DVB-C TT C-1500 (moved from the old system)
- mythtv 0.23.0+fixes

Well, when the new system runs for itself, theres no problem at all,
recordings are pretty well. But as soon as I'm starting streaming an
archived recording from the RAID to my TV (no matter if I do this via
NFS, UPnP or Samba) the recordings get bad. There are a lot of artefacts
and audio glitches in the recording. As soon as I stop streaming this
'noise' vanishes immediately. The same happens, when I'm  just copying
an archived recording to my notebook for example, or when I'm md5summing
any archived video-file on the RAID. It happens every time when I
generate any mentionable I/O load to the system.
It happens not, when I'm copying Files from external USB-HDD to the RAID.

I've searched this list and other for an explanation to this, but what
I've found on this topic are really old threads like this one:
http://www.gossamer-threads.com/lists/mythtv/users/159591 or this one:
http://pchdtv.com/forum/viewtopic.php?p=6378
These guy's troubles seem to be at least partially to be the same as
mine, except for the fact, that I have different hardware. In these and
other threads people are talking about RF-noise or EMI causing bad
reception to the tuner of the DVB card, when there's a higher I/O load
to the system. Others are suggesting playing with the PCI-latency as
described here: http://www.mythtv.org/wiki/PCI_Latency

What I did:
- I've tried playing around with the latency but without any effect. As
far as I'm understanding this, the SATA-controller is connected to the
PCIe, which is independent from the PCI-bus which holds the DVB-adaptor.
So it makes really sense to me that playing with the latency doesn't
have any effect on this issue.
- I've observed the reception level using femon while recording and
streaming the same time -> didn't see anything suspicious.
- I deactivated the onboard Realtek R8168 in BIOS and replaced it with
an Intel PCIe GBit card -> no effekt
- I shut down mythtv-backend and tried DVB live-tv with me-tv -> same
effekt, picture gets corrupted

What I've observed:
- CPU-load never seemed to be at any critical rate while recording and
streaming
- Playing around with different Kernels from 2.6.32 to 2.6.38 - no
matter if with their own dvb-modules or newest ones from linuxtv.org -
it makes no difference
- There are only few BIOS-versions available for this board. No matter
which one I try, it makes no difference at all
- syslog shows no errors
- backend.log contains many errors of these: 2011-09-18 21:33:59.617
Error: offset>181, pes length & current can not be queried. Except for
these there are no other errors during recording and streaming at the
same time
- 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
2011-09-19 14:43:46.367 [ac3 @ 0x8699960]frame CRC mismatch
2011-09-19 14:43:46.368 [ac3 @ 0x8699960]frame sync error
2011-09-19 14:43:46.368 AFD Error: Unknown audio decoding error
2011-09-19 14:43:46.370 [ac3 @ 0x8699960]frame CRC mismatch
2011-09-19 14:43:46.618 [ac3 @ 0x8699960]frame sync error

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. 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 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.