[mythtv-users] Fwd: Pixelation/Bad Recordings HDHR Prime -- I am at my wits end

[Frank Feuerbacher]

On 13-09-12 02:41 PM, Captain Hook wrote:
> <Snip>
> I know you can use RDM devices, but it doesn't seem to easily allow me
> to do this with onboard storage.  There are options for iSCSI/SAN
> devices, but I see in the link it may be possible, although it seems
> unclear if they've actually added an add-in controller card or not.
>
> I am using virtual disks, yes.  They are added through vSphere which
> then carves up the physical disk and creates VMDKs presented to my
> VMs.
>
> I've run a few benchmarks against these disks in the VMs and I don't
> really see much in the way of poor performance.  It is my
> understanding that recordings really don't take much in the way of
> performance and you can easily use even 5400 RPM drives with multiple
> simultaneous recordings.  My recordings thus far have almost
> exclusively been one at a time.
>
> I am using ESXi because I am very familiar with it and like to run
> multiple OSes and use it's capabilities (snapshots, migrating data,
> etc.).  I built a fairly decent performing server hoping to be able to
> utilize one box for everything.  I am using Windows Server because I
> run an MS shop in the day time and wanted a domain at home.
>
> I will consider running Ubuntu on the box and then using another
> virtualization method, but I'd really like to avoid that if possible.
> _______________________________________________
I have a 4 CPU 2.6Ghz HD4000 Ubuntu box with 16G ram. It has 3 spindles 
and I thought I was in good shape cpu, gpu and disk throughput wise. 
However, I was a little sloppy about some of my processes and got 
pixelation problems at times. The core problem was i/o. The machine 
mostly runs mythtv to record 1 or 2 HD content shows (Ceton infinTV 
card). It also encodes shows using Handbrake to .mkv.

One spindle is my root and home filesystems (also where handbrakes 
writes encoded movies)
One spindle is for mythtv and the scratch area for editing/trimming movies
One spindle is my movie repository for XBMC

One of the mistakes that I made was having mythtv perform commercial 
detection after a show was recorded instead of during the recording. 
This triples the I/O on the same spindle. I also copied the recording to 
a scratch area (on the same spindle) for manual trimming and Handbraking 
instead of creating a symlink (which meant each recording had another 
read/write pass). I also ran avidemux to build an index on each 
recording to save me time later. Finally, I had all of these operations 
running at the "normal" I/O and cpu priority.

To fix, I changed commercial detection to run during recording. I 
changed to use symlinks and I modified my job script to run avidemux 
with lower I/O and cpu priority using:*
*

    *ionice -c idle -t /usr/bin/nice -n10* <command>

Similarly, I lowered the priority of my handbrake scripts. I also have 
mythbackend running with a nice value of -5. After these changes I have 
not encountered any problems. If I did have trouble, the next thing I 
would do is move my scratch copies of shows to another drive. This would 
mean that the mythtv drive would have two passes over each recording one 
to write and one to read it for copying to another drive. I don't think 
I have tried increasing any buffer caches. It might help.

Finally, I also had problems with the cable signal strength. I proved 
this using the signal strength reading from my InfiniTV card. The cable 
company concurred and added an amplifier, but the signal strength varied 
significantly over the bandwidth so they had to add an attenuator for 
some frequency ranges. Anyway, you do have to pay close attention to the 
use of splitters, and you seem to have quite a few. Your cable modem 
probably needs special handling, but all of your video devices should 
receive the same signal strength. If you have 5 video receivers, then 
you are much better off with a 5-way splitter (ignoring the cable modem) 
than to have a tree of splitters. Make sure they are good splitters and 
not Home Depot specials.

Good luck.

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.mythtv.org/pipermail/mythtv-users/attachments/20130913/f9681bfa/attachment.html>