[mythtv-users] Video breaking up after installing new video card

[Mike Perkins]

On 03/05/14 10:31, Karl Dietz wrote:
> On 03.05.2014 10:52, Mike Perkins wrote:
>> On 03/05/14 00:45, Phill Edwards wrote:
>>>
>>> I'm using a HD Homerun with DVB-T broadcasts. Recently I also installed a
>>> DVB-T PCI card to get more simultaneous recordings. Is the problem more
>>> likely to be signal strength or I/O bottleneck? I guess signal
>>> strength can
>>> be fixed with some sort of boost device, but an I/O bottleneck would mean
>>> buying faster disks.
>>>
>> No! To fix an I/O bottleneck you may require *more* disks, not faster
>> ones. This reduces head thrashing while attempting to record/play more
>> than one stream at a time. (To my mind, the ideal is: # disks == max #
>> tuner streams.)
>
> No, too! ;) You also need enough free space on the existing file systems so the
> file system doesn't have to split writes all over the platter.
>
> Do not set your backend to fill your file systems to the point where
> fragmentation kills performance due to the amount of head movement needed to
> read/write the recordings.
>
> You may also add a disk for the database to your ideal figure. And is a tuner
> stream one service or one multiplex?
>
> Or a dedicated network connection between HDHR and backend.
>
> Or give the PCI card a dedicated IRQ to avoid potential issues with IRQ sharing.
>
>> Having said that, if the bottleneck is in the motherboard chipset or OS
>> disk caching, more or faster disks won't help. You'll need to analyse
>> exactly *what* the problem is before you start spending money on the
>> wrong solution.
>
> +1 on finding the bottle neck / problem before trying random solutions that may
> or may not be related to the symptoms.
>
As regards fragmentation, of course these would be writes to drives dedicated as 
mythtv storage directories. All the files are going to be very large which means 
that deletes are going to leave large holes as well. I'm not concerned about 
fragmentation.

For 'tuner streams' I obviously meant streams as written to disk. I don't know 
of anyone who writes entire multiplexes to disk. 1 stream -> one program.

-- 

Mike Perkins