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Andrew Pollock

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Sunday, 13 August 2006

Found one small problem with using ATA over Ethernet

And I can't believe I'm the only person who's struck this, but so far Google hasn't turned up any useful leads.

The problem is pretty obvious, when the system boots (well Debian Etch at least), it runs mountall.sh at priority 35 in /etc/rcS.d. That tries to mount all the local filesystems (it does the determination for what is locate or remote by the filesystem type in /etc/fstab, there's a hard-coded list of filesystem types to explicitly not try and mount). Then the network comes up at priority 39. The problem's rather obvious.

I did a reboot test tonight to see if everything would load and come up correctly on reboot, and well, it didn't even boot up properly, because /srv couldn't be fscked, let alone mounted, and that's my AoE volume.

My /etc/fstab contains:

/dev/etherd/e0.0        /srv    jfs     defaults        0       0

The problem is, as far as the init scripts are concerned, based on filesystem-type, this is a local filesystem. The init scripts don't have the concept of a remote block device. I tried moving all the networking initialisation scripts before the mountall.sh script, but think there's an inherent delay between the network coming up and the aoe driver figuring out what shelves and slots are actually available and creating the relevant entries in /dev/etherd

The thing is, this seems to be a rather essential thing that I'm trying to do, so I can't believe I'm the first person to run into this. I'll sleep on it and see if the lazyweb comes up with anything...

[23:32] [tech] [permalink]

MythTV in under 24 hours

Last night, the final component of my MythTV setup arrived - the TV tuner card, a Hauppauge WinTV-PVR-350. I'd had the other bits and pieces for about a week, indeed I'd already had MythTV installed and "operational", but there's really only so much you can do without a TV signal in the mix as well.

So I had a bit of a late night last night bashing on things and getting it all going. It was actually surprisingly trouble-free.

For some reason, I naively thought that the more contemporary 2.6 kernels had all the support required for the PVR-350. Not true. You need to grab the ivtv driver and build it separately. If I was less impatient, I would have worked with module-assistant to get it packaged, but I just threw it on. I have to run 2.6.17 to get the sound working, so I needed the 0.7.0 version of the driver. This built and installed fine, and I could run mplayer against /dev/video0 and see (and hear) TV fine. With a bit of tweaking of MythTV, it was happily using the card.

Getting the remote control to work was slightly more problematic. It turned out that I needed to get the latest greatest lirc from CVS in order to get everything to build correctly, and get a /dev/lirc that I could actually read from. After that, everything else just fell into place.

The last thing I spent a bit of time battling with today was guide data and channel tuning. It seems for some reason that channels greater than or equal to 14 didn't have their frequency set correctly, so I had to manually edit each channel and put in the frequency in kilohertz that ivtv-tune --list-channels provided. The Zap2it chaps also provide two different sets of guide data for Mountain View, and depending on which one you pick, you get a totally screwed up idea of the actual channels available. I also discovered the hard way that changing from one set of channels to the other without cleaning out the channels first leads to a complete mish-mash of channel data that correlates even less with reality than choosing one or the other by itself.

But within 24 hours of receiving the tuner card, I have everything up and running. The ATA over Ethernet disk array (that Myth tells me is good for over 600 hours of recording) seems to be holding up to the task alright. The current bandwidth utilisation for a few test recordings is interesting:

Graph of bandwidth utilisation for disks attached to the MythTV server
via ATA over Ethernet

So it seems that a TV show is a nice steady 5 mbits/sec, which everything seems to keep up with okay. The post-processing to flag commercials seems a bit more bandwidth-intensive. It seems to take about 40 minutes to flag the commercials for a 60 minute block of recording.

It's early days yet, but I'm fairly happy with how everything's operating so far. I can certainly leave things as they are for a while without needing to fiddle with things any further.

The one thing I do want to mention is the guide data. The fact that it's totally free, and designed to be used by the likes of MythTV is awesome. PVRs really live and die by the guide data, and it's so cool that Zap2it offer it completely gratis. Mad props to them.

Oh, and while I'm dishing out praise, I really must also thank Christian Marillat for http://www.debian-multimedia.org/ and for packaging up MythTV for Debian. If I had to build all of this myself, I'm sure it wouldn't have been so trouble free.

[00:01] [tech] [permalink]