[mythtv-users] Some real-life HDTV bandwidth/reliability observations
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 
> * 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  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
> * 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.)
>  Please see the list archives for why I use CIFS and not NFS.
>  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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> mythtv-users at mythtv.org
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