[Tig] Minimum RAID bandwidth for 2K playback?

[Bob Friesenhahn]

On Fri, 18 Jul 2008, Jason Howard wrote:
>
> We use 3ware (9550/9650/9690) controllers with either SAS or SATA in Raid 0,
> Raid 5, or Raid 1+0.  Arrays are usually 12 drives, but that is usually due
> to capacity.  We have found that the 3ware controllers scale pretty linearly
> (in both reads and writes) until about 10 or 11 drives.

I have heard lots of positive things regarding 3ware controllers.  I 
assume that the scaling issue is due to backplane slot bandwidth 
limits, or perhaps an on-board limit.

> Other than that, there is a bit of tuning in terms of read ahead.  It also
> helps when your application is able to tell the OS when not to cache a
> particular read or write.  As it turns out, a significant bottleneck can be
> the OS in trying to cache (and dump cache) while reading and writing-
> especially since in a typical playback/record scenerio, you won't really need
> that frame again.

Yes.  The OS I use (Solaris) does very aggressive caching and this is 
indeed a factor, but even more for writing than reading.  I believe 
that there is a way to tell the OS not to cache at all.

Unfortunately, my own software is not designed for real time playback 
even though the FPS is sufficient at the reader level. Are you aware 
of some open source software which can deal with real-time HD/2K 
playback directly from DPX files?  It seems that such software can be 
dramatically smaller than my own.

Bob
======================================
Bob Friesenhahn
bfriesen at simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/