Re: SATA-performance: Linux vs. FreeBSD

["Martin A. Fink" <fink@mpe.mpg.de>]

Am Dienstag, 13. Februar 2007 13:24 schrieben Sie:
> Martin A. Fink wrote:
> 
> >> Also you have skipped the information how the images "arrive" on the 
system 
> > (PCI(e) card?), that may be important for an "end to end" view of the 
> > problem.
> > 
> > Images arrive via Gigabit Ethernet. GigE Vision standard. (PCIe x4)
> 
> The the next question is: ChipSet/Used Protocol/JumboFrames/(NAPI)/... .
> 
> Have you already determined the load caused by this part?
> Depending on the GigE-Chipset, and Protocol/JumboFrames/(NAPI)/..., the 
involved overhead can be quite serious.
> 
> >> And what's also missing. What is "a long period of time".
> >> Calculating best-case with the SSD:
> >> 27GB divided by 30MB/s only gives a bit more than 15 Minutes.
> >> And worst case with 50MB/s is less than 10 Minutes.
> > 
> > Well. The testdrive has 27GB. The final drive will have 225 GB. And there 
will 
> > be 3 cameras and thus 3 disks. This means we talk about 140 MB/s for 
around 
> > 90 minutes.
> > For space applications with low power but high performance this is a long 
> > time... ;-)
> 
> The MB/CPU/RAM will be the one specified in the first mail?
> My gut feeling says: Forget it.
> 
> The needed total bandwidth may be to high and at least the incoming part via 
GigE may have serious overhead.
> 150MB/s in via (at least 2) GigE, without Zero-Copy there is another 150MB/s 
memory to memory.
> Then there is the next 150MB/s memory to the discs, without Zero-Copy there 
also another 150MB/s memory to memory.
> In total that's 300MB/s to 600MB/s without any processing.

I dont understand your calculation: from 3 GE ports come around 50 MB/each. 
These altogether 150MB/s have to be copied to memory. From there they will be 
copied to disk. So we talk about 2x150 MB/s running through my system. That 
is less than 2 PCIe lanes can handle... And there are more than 2 lanes 
between north and south bridge....
> 
> But on the other hand, hdparm -T says my system (Core2Duo E6700, FSB1066, 
2GB DDR2-800 RAM, 32Bit) has a buffer-cache bandwidth around 4000MB/s.
> As you don't said which FSB and Memory-Type you have i would guess that your 
system should reach between 2000MB/s and 3500MB/s of LINEAR(!) memory 
bandwidth.
> (Total usable Memory-Bandwidth is unfortunately also dependent on usage 
pattern. Large & linear is not as important as with a rotating HDD, but it 
factors in)
> 
> 
> 
> Btw. On the topic of filesystem and Linux performance:
> SGI did a "really big" test some time ago width a big iron having 24 
Itanium2-CPUs in 12 nodes, and 12*2 GB of ram and having 256 discs using 
XFS(Which is from SGI!).
> The pdf-file is here:
> http://oss.sgi.com/projects/xfs/papers/ols2006/ols-2006-paper.pdf
> 
> According the the paper the system had a theoretical peak IO-performance of 
11.5 GB/s and practically peaked at 10.7GB/s reading and 8.9GB/s writing.
> IOW Linux and XFS CAN perform quite well, but the system has to have enough 
muscle for the job.
> And since the paper (and Kernel 2.6.5) the development of Linux hasn't 
stopped.
> 
> 
> 
> -- 
> Real Programmers consider "what you see is what you get" to be just as
> bad a concept in Text Editors as it is in women. No, the Real Programmer
> wants a "you asked for it, you got it" text editor -- complicated,
> cryptic, powerful, unforgiving, dangerous.
> 
> 

-- 
Dipl. Physiker
Martin Anton Fink
Max Planck Institute for extraterrestrial Physics
Giessenbachstrasse
85741 Garching
Germany
Tel. +49-(0)89-30000-3645
Fax. +49-(0)89-30000-3569
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