[Madlug] Tracking Down Network Sags

[Mark Felder]

I'd go with number 3.

Honestly mixing MTUs and cheap switches are likely the problem.  
Consumer grade network hardware sucks....

Mark

On Aug 13, 2009, at 11:13, Timm Murray <tmurray-mlug at wumpus-cave.net>  
wrote:

> I have a Linux file server holding most of my movie collection,  
> along with a Mac
> Mini used as a HTPC, both with gigabit ethernet.  There are two  
> switches in
> between them, both of which support jumbo frames.  The Mac is set to  
> MTU 9000
> and the server set to 7200 (the max MTU the respective switches and  
> NICs
> support).  File transfer is done over SMB.
>
> Playback is smooth for most of any given movie, but there are sudden  
> sags at
> various times.  This happens to anything from a DVD rip up to a  
> 1080p vid.
>
> Theoretical max speed of a gigabit network is 125 MB/s.  Using ttcp  
> between the
> two machines above, I was able to get some decent real world  
> throughput figures.
> Dumping 500MB from /dev/zero from the Mac to the server gets 93.77  
> MB/sec.
> Dumping a 500MB file from the hard drive gets 22.36 MB/sec.
>
> According to wiki, the maximum bitrate of a Blu-ray video is 54 Mb/ 
> s, or 6.75
> MB/s, which is an upper limit.  Most any 1080p movie is going to use  
> VBR, and a
> lot of the movies I'm having problems with probably have closer to 1  
> MB/s
> bitrate (DVDs max at 10 Mb/s, or 1.25 MB/s).  I ought to have plenty  
> of overhead
> left over.
>
> Something must be intermittently flooding the switches with data.   
> There are a
> few other machines on the network that could be culpable.  I tried  
> running
> wireshark to pick out any traffic spikes, but nothing stood out (and  
> it's a very
> hit-or-miss approach, in any case).  I know SMB can be pretty  
> chatty, but it
> shouldn't be so chatty that it saturates a gigabit network.
>
> I've been copying the files to the local disk before playing and  
> then deleting
> when I'm done, but that negates the convenience of not swapping disks.
>
> Things I'm thinking about trying:
>
> 1) Switches are cheep, buy new ones that don't suck
> 2) Coerce the video player into treating the movie as a network  
> stream rather
> than a local file so that it buffers the data
> 3) Writeup a GUI in Visual Basic and see if I can trace an IP address
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