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PostPosted: Thu Oct 29, 2009 2:45 pm 
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How many HD streams can one hard drive handle? I currently have a single HDHomerun (dual tuner) streaming OTA HD to my mythbox, which is a combined frontend/backend 2.4GHZ dual core AMD with a single hard drive dedicated to recordings and one dedicated to the OS. Can my single drive handle recording 4 HD streams while watching a 5th? The recording drive is a 1TB WD Carver Black 7200rpm.

I only record OTA tv, no cable or satellite. The wife has asked if I can add more tuners (another dual tuner HDHomerun) and I am just not sure.

Thanks

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PostPosted: Thu Oct 29, 2009 3:18 pm 
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I don't see you having a problem.

I can record 4 HD streams, 2 from a HDHR and 2 from HD-PVRs. It's a little different than you since all of yours will be network based but I would think you would not have a problem. I know I've recorded 4 programs and watched at least 2 streams with not a hiccup.

My backend is a 3.0GHZ single core Intel (circa 2004). And a similar drive.

I'd mostly worry about splitting the OTA antenna two more times!


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PostPosted: Thu Oct 29, 2009 4:46 pm 
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Location: middleton wi usa atsc
I think the bottle neck to be concerned about is network bandwidth. Does your router allow you to monitor your bandwidth while you are recording 2 HD streams? Is your frontend on a different box, that would add to the network load while watching another stream.

Another data point:
I can record 2 HD shows from an hdhr and a third from a pci card tuner and watch a forth show, all on a combined frontend backend machine with a 1 TB drive. 3.2ghz p4


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PostPosted: Thu Oct 29, 2009 6:38 pm 
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Location: Madison, WI
ATSC has a max bandwidth of about 18 Mb/s (not sure if that's directly translated to network stream).

If it is, then an HD homerun could have a max bandwidth requirement of 36 Mb/s. This is just over 1/3 of the 100 Mb/s network connection on the HDHR.

2 HDHR's could theoretically need 72 Mb/s. This could be a problem on a home 100 Mb/s network.
This should be no problem if your home network was gigabit.

I typically get 250 Mb/s transfer rates to/from my box to my pc when copying recorded shows over my gigabit network. I don't have jumbo frames enabled and have never tried to optimize my network speed.

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PostPosted: Sun Nov 01, 2009 10:22 am 
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Thanks for the input. I have another hdhomerun on the way. I will let you know how it turns out.

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PostPosted: Sun Nov 01, 2009 11:12 am 
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I'll be interested to hear how it works out. If worse comes to worse, maybe you could add another network card just for hdhr.?.


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PostPosted: Sun Nov 01, 2009 11:30 am 
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I'm interested too !

my experience is like the others in that I can make 4 recordings on one machine- 2 from the internal tuner cards, and two from the hdhr...

Now the hdhr works so well, I'd like to get another to feed a different mythbox, but I have a 100 eithernet, not gigabit, and think the next step is bumping up against it's limits....


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 Post subject: two NICs
PostPosted: Tue Nov 03, 2009 11:51 pm 
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If the HDHR only need to be seen by the LinHES box buy two more network cards or onemore and another router. I'm assuming that you could set up an HDHR as an AdHoc network for that first option.

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PostPosted: Wed Nov 04, 2009 11:48 am 
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I remember reading something a while back on how the hard drive bottlenecks a gigabit connection sooner than one might think... <digs it out> ah here is the relevant page:
http://www.tomshardware.com/reviews/gig ... 321-4.html

So if we take the 45MB/s (360Mb/s) realistic rate for the HD from the article and the bandwidth figures quoted above as reliable then the drive should be good for 4+1, but I would expect that's pretty close to the limit, even though it's only half the drive rate. That's because that speed is for a constant single-file transfer, but if your BE is writing 4 files and serving up a 5th all at once the drive is going to perform significantly slower due to all the seeking back and forth.


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PostPosted: Wed Nov 04, 2009 12:52 pm 
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paulsid wrote:
So if we take the 45MB/s (360Mb/s) realistic rate for the HD from the article and the bandwidth figures quoted above as reliable then the drive should be good for 4+1, but I would expect that's pretty close to the limit, even though it's only half the drive rate.

Now I admit in advance that this algebra stuff sometimes messes with my head. But if we round up the transfer rate of an HD stream to 20Mbits/sec, then five of the suckers (4 in, 1 out) would account for 80Mbits/sec in and 20Mbits/sec out. That ought to be easy for a drive able to handle 360Mbits/sec.

Yogi Berra once said "90% of this game is half mental!" This topic reminds me of that...

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PostPosted: Wed Nov 04, 2009 2:07 pm 
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Location: Calgary, Canada
Liv2Cod wrote:
But if we round up the transfer rate of an HD stream to 20Mbits/sec, then five of the suckers (4 in, 1 out) would account for 80Mbits/sec in and 20Mbits/sec out. That ought to be easy for a drive able to handle 360Mbits/sec.

Yes but I was going by this figure:
jimdoc wrote:
If it is, then an HD homerun could have a max bandwidth requirement of 36 Mb/s.

On reflection I'm not sure why it would take double the recording bandwidth but since I know nothing of how the HDHR works I'm not in a position to question how accurate the numbers are.

I'm actually just here 'cause I think it's an interesting theoretical problem. :)


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PostPosted: Wed Nov 04, 2009 3:05 pm 
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The HDHR has two tuners. The 36 Mbps number is accounting for two 18 Mbps streams.


I would think that two HDHRs would be possible over a good 100 Mbps connection assuming it doesn't have much additional traffic however this would be pushing 100 Mbps right up to it's practical limits.

Going gigabit would solve this problem. A gigabit connection should easily be able to handle 10+ HDHR boxes but you would need one heck of a storage setup to handle that kind of data input.

No question about it my Gigabit connection is limited by my hard disk. It tops out right at ~50 MBps same as my sustained read speeds on my SATA drive (not a coincidence). Sustained write speeds will be even less than the read speeds. I would say 35 MBps would be a reasonable "real world" estimate for a new SATA 3.0 Gbps drive's sustained write speed. Therefore, in theory, a new SATA 3.0 Gbps 7200 RPM drive could barely handle up to 7 HDHRs sending two streams each to it. Of course that doesn't take into account servicing the OS and any other programs / processes the disk must service.

All in all I believe a fast disk and a Gigabit connection could easily handle 3-4 HDHR's and quite possible more, especially if your /myth partition is on a separate disc from your OS.

Martian

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 Post subject:
PostPosted: Fri Nov 06, 2009 6:17 pm 
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I also decided to get a second HDHomerun to ease some conflicts. It arrived about an hour ago. I installed it along side my original and added via mythtv-setup.

Did a quick test. Recorded 4 HD streams, the remaining 9 minutes of the network national news. Then on one client watched last night "Supernatural" which also is in HD.

Not a hiccup on either watching the recording or any of the 4 recordings. The backend is a 3.0 single core Dell circa 2004. With your typical 1TB WD 7200RPM sata drive. I do have a gigabit switch for networking but to be honest it doesn't do a great job with mixing 100 and 1000 devices.

Just an FYI.


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 Post subject:
PostPosted: Fri Nov 13, 2009 4:09 pm 
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I installed the second HDhomerun and everything works just fine. I can now record 4 HD streams while watching a 5th.

I am using a gigabit switch, and I did have to add an amplifier to my OTA antenna.

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 Post subject:
PostPosted: Fri Nov 13, 2009 5:55 pm 
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Joker wrote:
I am using a gigabit switch
Does your Mythbox have a gig network card in it?


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