[mythtv-users] DVICO Fusion HDTV 5 Lite vs HD3000

Michael Haan michael.haan at gmail.com
Wed Jan 18 01:29:31 UTC 2006


On 1/17/06, Brandon Beattie <brandon+myth at linuxis.us> wrote:
>
> On Tue, Jan 17, 2006 at 05:11:08PM -0500, Michael Haan wrote:
> > I understand what you're saying.  The first thing I would note is that
> this
> > is QAM not satellite so trees etc aren't the issue.  The machine is an
> AMD64
> > 3800+ writing to a raid 5 array.  Granted, the array is software raid,
> but
> > watching live HD, my cpu hangs around 10-20%, so I think it's fine.  So,
> I'm
> > trying to figure out what to look at next.  One final point:  watching
> HD
> > through the HD3000 I get occasional pixelation but if I then switch over
> and
> > watch the same channel through firewire, there is no pixelation.  Just
> seems
> > like that points the the card.
>
> QAM can have even more problems than OTA, it just depends.  Do you use
> any splitter, powered splitter, or amplifier?  Do you have a cable
> modem?  Any one of those can cause attenuation or interference.  The
> fact that the cable box doesn't have problems could be that it has a
> better QAM tuner, or that it just works better for your specific cable
> provider.  I'd recommend calling the cable company and have them do a
> quality check (They can do this from remote and free of charge).  Also try
> disconnecting any splitters or cable modem and see if this helps.  The
> pcHDTV HD-3000 has had the best success in tuning the various types of
> QAM, so I'm not sure what else to recommend if you want a PCI HD tuner,
> but if firewire works perfectly, go for that. :)
>
> Also just so it's known, you can have the best system, raid 10, and
> still get corrupted video.  There are a few things that can cause
> this.  The update scheduled recordings task is nasty in Myth... and Mysql
> can be nasty too.  I see (Weekly) a single recording lose data when
> it spawns this task.  There has been a lot of time spent on tring to
> make this less severe.  I actually spent about 40+ hours with Daniel and
> others down to the point of profiling the kernel to help improve this
> problem.  To keep this from being as bad:
>
> Don't ever think about using ReiserFS.  Some disk accessing is slow
> first of all, such as deletes.  If you delete a large file it can keep
> the disk from writing for several seconds, by then Myth drops data.
> Also, reiserFS does not handle large files very well.  Combine a many GB
> file and a directory holding 1+TB of data in it and you're really going
> to have problems.  You don't see this as bad with few large files in a
> directory.
>
> Don't put your recordings directory on the same disk as where MySQL
> stores the DB for mythTV.  You can lose data when mysql is using the
> disk and doesn't let the mythfilewriter thread save data to the disk
> before it's taken too long and discarded the data.
>
> A few signs (But not always there when problems do happen and data is
> lost) are IO Errors/IO Bound.  Notices that it's taking too long to read
> data from the HD card, or you can enable debug and get a half dozen
> other errors that will show up when you have a thread struggling for
> resources.
>
> You also can see these problems with a CPU at 95% idle.  You can watch
> for the actualy system load, or the system io usage to help you see if
> this is too high and causing problems, but problems do happen even when
> this is low because the time between updates for top and other apps
> doesn't check fast enough to always see the io problems that could cause
> data to be lost.
>
> --Brandon
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>

Yes, there are two splitters between the source and the card - there is also
a cable modem and an amplifier.  You may be right that this is an
attenuation issue but the 3000 in the same rig with the same setup worked
almost flawlessly under a previous gentoo incarnation so that makes me
suspicious.  I am using reiser (just as I was before) - I could try
switching that but I'd need a recommendation for what to use.
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