Example of a 3 tuner system

[Narflex]

I just built a 2 tuner yesterday and a 3 tuner today for some folks. Thought I'd share the specs with you all in case you were interested in a powerful yet inexpensive configuration.

Base PC - Compaq S3100NX - includes XP 2200+ proc, 256MB RAM, 80 GB HD, LAN, sound, USB, serial, AGP, 3xPCI, XP Home, DVD-ROM/CD-RW
Hauppauge WinTV PVR 250 x 3
IBM 180GXP DeskStar HDD 120GB
PNY Technologies GeForce4 MX440-SE AGP Graphics card w/ TV-out
SageTV

That's one sweet 3-tuner system with 200GB of storage...can you believe it???? It's pretty amazing what you can build with a PC once someone writes the software to control it.

Thanks,

[edmc]

Jeff,

I'm curious if you think the 2nd Disk Drive is needed for performance what with 3 Tuners capturing while, possibly, one program is being played back. I mean, with 3 Tuners one might find a need for 200GB :-) but is the speed of a single drive sufficient for 4 simultaneous streams (3 being captured and 1 being played back)?

[jmeeks]

This brings up an interesting scenario.

Is there a way that each card could be mapped to a preferred drive if available in the Sage program to address this type of issue? What would be the maximum number of cards you could put in a system, before you saturate the bus, if you could handle the hard drive routing issue?

John

[edmc]

I think the problem isn't the bus (either PCI or IDE/SCSI/SerialATA/whatever) but rather the performance of the spindle itself. Drives accessed Randomly perform significantly worse than when accessed sequentiually. So, even if the Transport Streams are written to contiguous sectors (which, being allocated within a general purpose FileSystem such as NTFS or FAT they are not), the fact that multiple Streams are being accessed means that a single Drive will be being accessed roughly randomly.

The concern is both for Bandwidth as well as I/Os per Second I suppose. I spend most of my time working with high end Storage Systems and FibreChannel Drives which, each, are usually significantly higher performing that the lowly IDE Drive in my HTPC.

In my case, recording 2 Streams simultaneously to a single Barracuda 80GB IDE Drive seems to work great. I have noticed some issues with Playing back one of the Streams while Recording two, but I haven't gotten a handle on it yet. I see absolutently no problems Playing one Program while Recording another with either one or two Tuner Cards.

[JJarmoc]

I imagine drive performance will get to be a larger problem if/when HDTV is supported. HD Streams are larger and much higher bitrate, so it seems that having mutliple streams floating around at once would cause an even larger burden on the bus and the drive itself. If there's serious concern over a problem with 3 SD streams, I can't imagine that 3 HD streams would be possible..

[Narflex]

The second disk was only for storage, not because of disk bandwidth.

I've found that if you format the disks with 64K block sizes and have the video folders for SageTV be dedicated partitions; you'll have no problems at all, even when doing a half dozen streams at the same time.

Here's a little math on it:
- MPEG2 stream is 6Mbps for Great quality
- a 64K block will contain 85 msec of data and will take ~1msec to read and up to ~15 msec to seek to it; and this is when the disk is at maximum fragmentation
- 85/16 ~= 5 simultaneous streams accessing the disk should still work

If you consider that in the worst case; the disk would never get completely fragmented you can increase that number by a few factors.

I used to really worry about the disk. But once I started using dedicated partitions with 64K blocks, I never see any glitches due to fragmentation. Even with 4 streams writing and 3 reading simultaneously....(that's testing stuff you don't know about yet). But other applications suffer signficantly in this state since disk access overall will be slowed down greatly; but it'll still be able to handle the throughput and Sage won't miss a beat.

[JJarmoc]

"Even with 4 streams writing and 3 reading simultaneously....(that's testing stuff you don't know about yet). "

Hmm.. you're pracitcally begging for guesses. Some sort of PIP feature?

[Narflex]

Nope, it's not PIP. It has to do with networking.

[dkardatzke]

Coming Soon...Networking and Streaming

[Mark Lamutt]

That's what I like to hear!

[JJarmoc]

Sounds nice! Any idea what sort of bandwidth it'll need though? I'm running my HTPC wirelessly to avoid having to run cables (in an apartment.. not a pretty situation) but I worry about 802.11b being able to support that. g devices are starting to appear but I can't find a decent g bridge yet.

HD Support would be even nicer though :-)

[SHS]

JJarmoc Picture-in-Picture (PiP) is a cool feature and it dose need multiple tuner, multiple stream, multiple overlay.
I know this PiP can be done with with Reg AVI card but MPEG I think that going need some major hosepower to do multiple decoding.

[Narflex]

Bandwidth will depend upon how many streams you want to run at once and of what quality level. Good quality MPEG2 (basically can't tell it apart from live TV) is about 6 Mbps.

[JJarmoc]

Thanks Jeff, that answers my question.. sounds like it's doable in at least some form over 802.11b. Nice to know.

As for PIP, it's a cool feature but I've had TVs that've had PIP and rarely have used it. The one thing it's nice for is channel surfing during commercials of something I don't want to miss, but PVRs have pretty much eliminated that from my routine. I really don't see much need for PIP anymore. It was really just the first thing I thought of that would mean having a good number of streams active at once. I really don't care one way or the other if it's in SageTV.

Did I mention I'd really like some kind of HD support though? heh..