The XO-1.5 software plan.

[Tiago Marques]

On Sat, May 16, 2009 at 10:54 PM, Chris Ball <cjb at laptop.org> wrote:

> Hi Ben,
>
>   > Of course, this equation gets still more complicated depending on
>   > whether we have MTD or FTL flash.  Choosing a filesystem will be
>   > an interesting exercise.
>
> I think it's clear that we'll be using an FTL of some kind.  (Which
> kind in particular will depend on more testing with the new A-Test
> board.)
>
> So, as a strawman, I'll suggest uncompressed ext2.  Depending on the
> FTL, something else may be more reasonable instead.
>

This is what I've been using on SD cards, USB drives, etc, with some
success. Seems stable enough, while helping out with wear.

Ext3 might be used with some tweaks:

http://thunk.org/tytso/blog/2009/03/01/ssds-journaling-and-noatimerelatime/

>From my experience XFS is more efficient for filesystems of only 4GB but
would completely wear out flash a lot faster. Depending on the number of
files you have, you may run out of inodes or space with ext2/3, while XFS,
for instance, can make a better use of each block and dynamically allocate
inodes.

I had a particular Gentoo install of about 2.8GB that couldn't fit in a 4GB
USB drive with ext3 due to the number of files used (especially due to
portage, lack of inodes IIRC). XFS saved me about 300-400MB of space and
managed to fit everything there. It was slower as it was constantly
optimizing the usage of blocks and was unusable on this particular drive due
to the low random writes. Had to switch to an 8GB device with ext2, which
was at least an order of magnitude faster.
I have no idea if ext4 or something else are a better fit for this kind of
applications.

My current XO is running a Gentoo install with portage read-only as a
squashfs image, which takes up only 40MB, easily fitting the install in the
4GB SD card with ext2. No problems until now, haven't noticed any corruption
although it does get rather slow when it needs to write many files at once.

Best regards,

Tiago Marques



>
> - Chris.
> --
> Chris Ball   <cjb at laptop.org>
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