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I have a raspberry model B (the first one) and it acts as a DLNA server through my local network.

A few days ago I tried to watch a film streamed by the rasp, it was full hd and sometimes it used to lag.

I made this calculation: File size: 6GB -> 6000 MB Movie length: 2,20hh -> 140 min -> 8400 sec

6000/8400 = 0,7MB/s = 5,6 Mbps

This should be the maximum required bandwidth for the streaming, right? How could it be?

I know some raspberries have problems with LAN speed, but 6Mbps is ridiculous!

I thought the problem might be the processor, so I'm thinking of buying a newer Raspberry Pi 2. Could this help in your opinion?

What else could it be? I have the raspberry linked to the router via LAN, same with the PC so I'm not using wifi! Also, the video is stored in an external HDD (WD MyBook Essential 1TB) self-powered.

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TL;DR

I've only seen about 6-8Mbs sustained off my Raspberry Pis at most times. Plus these tiny devices are not great at transcoding video unless your setting up a cluster of them since these guys are no more powerful than an old AMD K7 from the late 1990's. In all cases check one's resource usage and limitations based on hardware specs.

Debugging

First step should one should alwasy do is debugging on your existing PI. By verifying any high level resource usage.

Try ssh into your Pi while streaming at type:

uptime && ifstat -i eth0 -q 1 1

From there one should be able to see the cpu load percentage for the past 1, 5 and 15 minute intervals and the KB/s network usage or eth0 (may need to change this depending on your distro).

If one is seeing anything around or above 1.0 in your load average then your doing the work of 100% of the available cpu resources.

Bottlenecks

Other things to take note of that can cause bottlenecks;

  • if one is using a CAT 5, CAT5e, or CAT 6 cable on your network
  • if Jumbo Frames are enabled, supported by all devices, and the software uses Jumbo Frames.
  • if there any POE on the line and/or other general networking topography that reduces network speed to the basic 10Mbs ethernet standard.
  • Any external HDD via usb has to drop down to 60MBps since the Pi only supports USB 2.0
  • If one's distro is compiled to use hardware floats or software floats for ARM processors. Soft floats run through software calculations instead of allowing the cpu to calculate thus adding more CPU time to a task.

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