[syslinux] mounting other compressed filesystems

Marc Haisenko haisenko at be-ok.com
Tue Sep 14 07:20:14 PDT 2004

On Tuesday 14 September 2004 16:17, Luke Albers wrote:
> I would like to have two compressed ext2 filesystems on my CF card, one
> for the root fs and the other smaller one to be mounted at /opt/XXX
> where I can compress what is in ram after modification and write it back
> to disk at regular intervals of time.
> can anyone tell me how I can do this?
> Thanks

Oooh, that's a hard one. Well, first thing that comes to mind is good old 
cron, but you're facing a big problem regardless of how you do it: what shall 
the routine that compresses the FS do when the FS changes while it is 
compressing ? You'll surely run into corrupted FS's sometime, I think.

The other thing to think about is that you should minimize writing to CF's 
because the more often you write to them the sooner they'll fail (thus if you 
have a FS on a CF you should mount it with the "noatime" option so that the 
FS driver doesn't write timestamps). This means writing to the CF in regular 
intervals is propably a bad idea.

I have an idea on how to solve this, maybe it suits you:

I guess that the stuff in /opt/xxx can be summarized into two categories: 
stuff that changes and stuff that's static. If the static stuff is taking up 
the majority of space you could do the following:

The root fs is a compressed image. It contains a compressed file trees (I'd 
use .cpio.bz2 for this). This compressed file tree gets extracted into a 
ramdisk and holds all your static stuff, let's say that this ramdisk is 
mounted at /static.

Then you have a normal, uncompressed partition which has symlinks into the 
/static tree.

Let's say your /opt/xxx looks like this:

/opt/xxx/bin/ -> /static/bin/
/opt/xxx/mixed/anotherstatic -> /static/mixed/anotherstatic

I hope you understand what I mean. This way all you're dealing with is 
read-only compressed data and uncompressed read/write data.


Marc Haisenko
Linux Solutions
Be O.K. service group GmbH

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D-80686 München
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e-mail: haisenko at be-ok.com

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