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Re: jffs2 vs nfs

+++ Oliver Kurth [05-04-18 12:17 -0700]:
> On Mon, 2005-04-18 at 15:15 -0400, ER wrote:
> > Hi all,
> > I've ran into some problems that some of you may be able to answer. I have my file system in flash using the jffs2 filesystem. I ran a simple application that accesses a network camera and spits out some data.
> > 
> > I've notice that when the jffs2 file system is considerably slower than the nfs filesystem. Is that normal? Not to mention that my application is also very much slower. 
> > 
> > What can be done? Is cramfs faster then jffs2?

It's not the FS - but RAM is generally _much_ faster than flash, so in
practice 'yes'. 

> > I'm considering loading the required libraries in RAM so as to speed up things (so I think atleast), will that be any help. I'm saying this although I haven't figured out how this works as yet.
> > 
> > My explaination is that the library access time (dynamically linked) is much slower on jffs2 than nfs but I'm still baffled why?!
> > Any my solution would be to have a ramfs which would be a copy of the flash filesystem.
> > Does that make any sense? Help???
> I do not know if it is faster, but maybe you can try this:
> http://www.aleph1.co.uk/yaffs/

Yaffs is significantly lower-resource than jffs2 because it is a lot
simpler. But a bit part of this simplicitly is that it does not compress
data the way jffs2 does so you get less on for a given amount of flash (or
need to compress the data itself, rather than expect the FS to do it for

This means that spoeed tradeoffs can be complicated. If it is the
flash-reading that is slow then reading compressed data can help.

Yaffs was designed for NAND flash - jffs2 was designed for NOR flash, and
ported to NAND. I'm not sure that this makes much practical difference any
more, but it is reflected inthe underlying decisions. 

> I haven't tested it myself, it is just a hint.

I doubt if it wil make much difference in this case, but people have
reported huge speedups changing changing from JFFS2 to YAFFS in some
circumstances. The one thing YAFFS is really slow at is having thousands of
files in one directory, although that will probably be fixed this week with
some smarter algorithms than a simple linked list. 

Aleph One Ltd, Bottisham, CAMBRIDGE, CB5 9BA, UK  Tel +44 (0) 1223 811679
work: http://www.aleph1.co.uk/     play: http://www.chaos.org.uk/~wookey/

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