[CUWiN-Dev] Flash Compression

[David Young]

On Mon, Mar 14, 2005 at 01:58:37PM -0600, Quantum Scientific wrote:
> On Monday 14 March 2005 12:53, David Young wrote:
> > CompactFlash cards do their own wear-leveling, so JFFS is not needed.
> 
> I don't think so, as most are NOR.  Wear levelling isn't so important though 
> when your system runs in ramdisk I suppose.

I am certain that CompactFlash cards do wear-levelling.  It is true that
we scarcely ever write to the CF card.

> But I believe you are using the flash as a block device (emulated), which 
> means you probably have two journalling file systems on top of one another 
> (depending on the drivers): one is the flash translation layer, and the other 
> is UFS-44bsd.  JFFS would be one journalling filesystem, and it has 
> compression as well.
> http://sourceware.org/jffs2/jffs2-html/node1.html
> Just a suggestion.  I do not know whether it would be bootable with just one 
> partition.

UFS is not a journalling filesystem.  As long as we're using CompactFlash,
JFFS is unneeded complexity.

> Another option to save space on flash, is compression of directory structures 
> into files on flash, with dynamic decompression on boot to ramdisk -- CIFS.  
> This is bootable with just one part.
> 
> If the system image could be reduced below 16MB, no hardware modification to 
> the Belkin or other router would be needed, to do remote updates.  I was 
> surprised to find the image is only 22.5MB now, so it may compress to 12MB.

It's true that things are fairly compressible.  Here is a list of
upgrade files in my home directory.  An upgrade file is a gzip'd tar
file containing the whole system,

% ls -l boot-image/*.tgz
-rw-r--r-- <snip> 9282828 Feb 19 21:55 boot-image/staboot-19-Feb-2005.tgz
-rw-r--r-- <snip> 9282933 Feb 20 23:01 boot-image/staboot-20-Feb-2005.tgz
-rw-r--r-- <snip> 9284523 Feb 21 03:14 boot-image/staboot-21-Feb-2005.tgz
-rw-r--r-- <snip> 9284387 Feb 22 21:35 boot-image/staboot-22-Feb-2005.tgz
-rw-r--r-- <snip> 9284359 Feb 23 14:27 boot-image/staboot-23-Feb-2005.tgz
-rw-r--r-- <snip> 9284488 Feb 24 21:10 boot-image/staboot-24-Feb-2005.tgz
-rw-r--r-- <snip> 9297242 Feb 28 18:05 boot-image/staboot-28-Feb-2005.tgz
-rw-r--r-- <snip> 9306692 Mar  2 00:03 boot-image/staboot-01-Mar-2005.tgz

Dave

-- 
David Young             OJC Technologies
dyoung at ojctech.com      Urbana, IL * (217) 278-3933