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Hardware Support Discussions related to using various hardware setups with SageTV products. Anything relating to capture cards, remotes, infrared receivers/transmitters, system compatibility or other hardware related problems or suggestions should be posted here.

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Old 11-18-2017, 07:18 AM
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Quote:
Originally Posted by texneus View Post
Math supports it. 20Mbps for a full bandwidth digital station (this is actually a bit generous, but the math is simpler). If there is a subchannel it will be lower than this.

20Mbps * 4 = 80Mbps. Even HDDs from quite a few years back exceed 100MBps (800Mbps) transfer rates, so recording from all four tuners uses about 10% of an HDDs throughput.

Toss in playback now. Say you're watching live (Does anyone do this anymore?) so there is a delay involved. Assume it's 2 seconds. I don't know what it really is but it's probably less than this. But if it were 2 seconds, there is 80Mbps going in, then 2 seconds later 80Mbps going back out. The amount of data written in those two seconds is 80Mbps * 2 = 160Mb or 20MB. So assuming your HDD has a 32MB cache (pretty typical now days to have at least this much), the disk, at least on paper, doesn't even need to read the data back from the platters since it would still exist in it's cache. Easy peasy.
Careful - I think those HDD transfer speeds you are referring to are for sequential read/write (typically 100-200MB/sec or 800-1600Mb/sec). But if you are recording multiple streams into separate files, the data probably isn't sequential. In this case the random read/write speeds probably come into play - those can be nearly 100 times slower. Smart caching algorithms in the drive might give a real world throughput somewhere in between.

In any case, just because there are multiple tuners in one device, there is no reason to limit yourself to one hard drive - you can spread the recordings over multiple drives whether you have 4 tuners in one device or 4 separate single tuner devices.

The only bottleneck I would worry about is the interface to the PC. There should be no worries with gigabit Ethernet or USB 3.x, but I would be worried if the interface was 100Mb Ethernet or USB 2.0.
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