[mythtv-users] recording drive bottle neck suggestions..

[Blammo]

On Mon, Aug 31, 2009 at 7:13 AM,
sonofzev at iinet.net.au<sonofzev at iinet.net.au> wrote:
> On Sunday night I ended up having a bottle neck as it was the first time I ever
> had 5 recordings going at one (1 HD 4 SD)... the system choked and I couldn't
> watch as the recordings were going (although it appears the recordings ended up
> fine).. The system couldn't seem to playback live TV or even a recording while it
> was being recorded without major stuttering (F1 race so it was important!!)
<snip>

Lots of good suggestions so far, a couple more.

1. If you're using Software Raid, consider a hardware card. I ran into
lots of issues trying to combine SWRaid with PCI-based tuners.  All of
that IO is CPU driven, and tens to not share nicely with things like
capture cards, ethernet cards (off-box flagged, playback etc) under
heavy loads. There was a good long period of time where SWraid + XFS +
NFS + HeavyIO meant lots of kernal crashes no matter which distro you
ran.

2. If you're using PCI based tuners, consider something external, like
HDHomerun if that's an option. The difference in IO Requirements
between 4 PCI tuners, and (2) external tuners is a huge amount...

3. Experiment with different IO Schedulers... I use the "Deadline"
scheduler.. it makes a profound difference for me being able to do
multiple streams plus flagging plus playback. You can change them
"live" on a given drive, see the results, then apply it as a runtime
option in your grub/lilo/etc boot config.  Here's a couple of decent
links describing them.
 ( http://www.wlug.org.nz/LinuxIoScheduler
http://archive.redhat.com/magazine/008jun05/features/schedulers/ )

What you want to accomplish is very possible.. lots of people on this
mailing list do. My backend records (6) HD while realtime commercial
flagging all 6, while feeding (2) HD playback, all with no issues.
(3ware Raid5, Opteron 275's, multiple drives)