[mythtv-users] Some real-life HDTV bandwidth/reliability observations

Mudit Wahal mwahal at gmail.com
Thu Jan 19 16:53:44 UTC 2006

I have two tuners, HD3000 and FusionLite5 and went thru similar issues
in sept/oct. The solution which worked for me was to increase
TFW_DEF_BUF_SIZE value to 32MB. There were other suggestions such as
using a different elevator program or file system. Once I changed the
variable to 32mb, all the IOBounds were history ! I still dont do any
commflagging or file deletion while recoding HDTV programs. Deleting
files on xfs is a breeze though compared to ext3. Search users/dev
list for the variable.

On 1/19/06, Yeechang Lee <ylee at pobox.com> wrote:
> Please consult the list archive for more on my setup. Quick recap:
> * Frontend/backend: 3.0GHz Hyperthreaded Pentium 4 with 512MB running
>   Fedora Core 4 and MythTV 0.18.1 from ATrpms
> * Program sources: Two Motorola DCT-6200 boxes through FireWire
>   (Point-to-point at 200Mbps).
> * MythTV storage: Infrant ReadyNAS 600 gigabit Ethernet-capable NAS in
>   ext3 over RAID 0, mounted via CIFS [1]
> * Network: D-Link PCI Express gigabit Ethernet card and SMC gigabit
>   Ethernet switch
> My experiences:
> * Frontend/backend (frontend presumably swapped out to disk, DPMS on)
>   and storage are idle: Two HDTV (from the premium movie channels,
>   say) programs record simultaneously without IOBOUND errors. One
>   high-bandwidth [2] HDTV program, or one high-bandwidth and one
>   regular HDTV, seems OK; I haven't empirically tested two yet, but
>   believe it should also be all right.
> * I'm watching a HDTV program and I'm also copying non-MythTV files
>   from the Infrant to another machine on the network: One HDTV program
>   and one non-HDTV program record simultaneously without IOBOUND
>   errors, generally speaking, except a burst for 4-6 seconds at
>   occasional five-minute multiples as Brandon Beattie and I have
>   discussed here recently. Two HDTV recordings at once result in
>   steady IOBOUND errors.
> * I delete a program from the frontend: A few lines of IOBOUND errors
>   regardless of what I am recording. Interestingly, deleting files
>   outside mythfrontend doesn't seem to be a problem, as I think I've
>   recently noted.
> * Frontend/backend is idle, and I'm also copying non-MythTV files from
>   the Infrant to another machine on the network: Two HDTV programs
>   record simultaneously without IOBOUND errors. One high-bandwidth
>   HDTV program (such as anything from HDNet) generates slightly more
>   serious (up to about 10 seconds) IOBOUND bursts at occasional
>   five-minute intervals.
> * A single medium-load commflag job is running and I'm also copying
>   non-MythTV files from the Infrant to another machine on the network:
>   One HDTV program records with 4 to 6-second IOBOUND bursts at
>   occasional five-minute multiples.
> Bandwidth use:
> * Digital non-HDTV channels generate the smallest files at about
>   900-1000MB/hour for a movie channel and up to 1200MB/hour for a
>   cartoon (with probably a lower-quality feed).
> * Analog channels such as TCM generate about 2900MB/hour due to the
>   extra noise. HDTV movie channels generate about
>   4400MB-4700MB/hour.
> * A high-bandwidth HDTV channel generates 7400-7700MB/hour . . .
> * Except for ABC (and, presumably, Fox), whose 720p programs record at
>   about 5.8GB/hour.
> Other notes:
> * I've seen the occasional mangled channel change (typically a digit
>   dropped) over FireWire when using live TV, but haven't seen it yet
>   with a recording.
> * I still *do* see the dreaded "recording previews fine but kills
>   mythfrontend on playback or at first OSD display [or at best, OSD
>   doesn't come up at all]" issue with perhaps one of every dozen
>   recordings. I haven't noticed any particular pattern regarding
>   channels, but this is my #1 annoyance with MythTV at the moment,
>   and--if I may plea to the developers and/or the ATrpms
>   packager--ample justification for an interim hotfix release for the
>   0.18.x series as opposed to having non-SVN users wait for the fix I
>   understand is in SVN to appear with 0.19. (By contrast, I can live
>   with "frontend crashes after two or three source changes during live
>   TV" and "changing channels in live TV mangles the sound, requiring
>   an escape and reentry into live TV to fix" issues; as an old TiVo
>   hand I know just how useless live TV generally is.)
> [1] Please see the list archives for why I use CIFS and not NFS.
> [2] Such as anything from HDNet or Discovery HD Theater and,
> interestingly, most network affiliates over cable. I presume OTA
> broadcasts' bandwidth demands would be even greater.
> --
> Yeechang Lee <ylee at pobox.com> | +1 650 776 7763 | San Francisco CA US
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