[mythtv-users] Is there a tuner limit? (problem with >8 tuners)

Janne Grunau janne-mythtvusers at grunau.be
Tue Aug 21 14:10:25 UTC 2007

On Tuesday 21 August 2007 14:31:47 Chris Wilkie - NetrinoUK wrote:
> Just to update everyone, I have solved the problem on advice from
> Robin and Janne .... Thanks guys!


> Next problem is that Myth's GUI doesn't let you select a DVB ID above
> 7, so a bit of database hacking was required.  I just added four
> extra cards on ID 7, then 'update capturecard set videoid=<8-11>
> where cardid=<9-12>'.  The GUI isn't happy if you try to edit those
> cards, but now it's all set up there's no need.

And patching that wouldn't be hard.

> I'm also using the PAE kernel in order to make use of the 16GB
> available RAM in the box.  The Nova-T 500 seems fine on this kernel
> (I was worried, after reading about freezes/lockups on some kernels
> with this card).

Are the Xeons 64-bit cappable? If yes, you should use a 64-bit system 
PAE is a dirty workaround. BTW I hope the server has more to do than 
recording and serving recordings. A single dual core with 2gb memory is 
already oversized for this task. The only benefit your big iron may 
have (I wasn't able to find docs for a HP DL720) is that it has more 
than one PCI bus.

> Now the problem I'm having is write speed on the disk array.  When
> making 8+ recordings, the load average (and io wait) shoots up.  It
> would appear that Linux is seeing the server's RAID system and
> switching the software write cache off, except that this server
> (apparently) doesn't have a write cache.  I guess performing 8+
> random writes to disk at 5-7MBit/sec each is causing the problem.  If
> anyone knows how to force the software write cache back on (to save
> me some google time finding out) please let me know! :)

How is the disk-array connected? through a PCI card/controller on the 
same bus as the Novas?

> The multi-rec brand looks a bit vague, certainly way over my level of
> understanding.  I was also only able to find very little information
> about whether it is stable, or even whether it works at all.  In this
> application, the system just needs to work, so I didn't want to mess
> around with development code.

It is stable and it works mainly. I have patches pending which makes it 
useable. So I would advise everyone who wants to use it to wait a 
couple of days.

> To be honest, I'm throwing away most of the functionality of Myth
> anyway, so I was considering just knocking up some Perl scripts to
> use with DVBTools, meaning I could do multi recordings from a single
> tuner, and doing away with Myth altogether.  All it needs to do is
> record programs to disk from a schedule - I don't need any of the
> other functions.  Maybe one day I'll get around to it, but for the
> moment Myth is doing the job just fine and 12 tuners is plenty. 
> We're running fine on 5 at the moment, but the recordings miss a lot
> of program start and end points, as I'm not able to give it extra
> time at the start and end of the shows.

This will be solved with the multirec branch.


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