[maemo-developers] [maemo-developers] Re: Span filesystem across both SD cards?

[From: Matan Ziv-Av]

Jon Smirl <jonsmirl <at> gmail.com> writes:

> 
> On 2/1/07, Neil MacLeod <gmane <at> nmacleod.com> wrote:
> > This may be a crazy idea, but what possibilities exist to span a single
filesystem across the two SD cards,
> thus presenting a single filesystem to the N800?
> >
> > I can imagine one day wanting to put a 500Mb media file onto the N800, and
having 300Mb free on each SD card
> would mean the N800 doesn't have enough contiguous space to store the file.
> >
> > Would it be possible to mount partitions on the SD-card in such a way that
the N800 could make the space
> available as one single filesystem partition?
> 
> The ability already exists in Linux. You need to turn on device mapper
> in your kernel and then use LVM2 or  EVMS.


LVM does not make a lot of sense for this, as it would create a card that is not
usable in other systems. I think unionfs fits this job, and also has the
advantage of not requiring kernel replacement, only a module load.

Need to add something like:

insmod unionfs.ko
mount -t unionfs -o dirs=/media/mmc1/usr=rw:/usr=ro unionfs /usr

to startup scripts (early enough) before anything opens a file for writing under
/usr.

See here:

http://www.linux-live.org/unionfs/

-- 
Matan Ziv-Av.    matan at svgalib.org