Re: Best filesystem for a CF card

On Tue, 28 Aug 2001, Michael Scott Shappe wrote:

> > Should it be JFFS2, ext2, ext3, or reiserfs? Any other types that I
> > might have missed that work well?
>
> The word that's circulated the last couple of times this has come up is that
> you should just go ahead and use VFAT unless you really need the Unixisms.
> CF is designed with a FAT-related FS in mind.
>
> If you do need the Unixims, the recommendation is to stick with ext2.
> Apparently both ext3 and reiserfs require a fair chunk of space for their
> journal, which negates any utility they'd have in minimizing flash wear.

Over 20MB for reiserfs IIRC, something like 10MB for ext3 but configurable
for ext3 IIRC...

> JFFS2 won't work out-of-the-box with a CF card becase CF cards present
> themselves as disk drives, not MTDs. Someone hinted at a way to make JFFS2
> work, but the hint wasn't enough for me to understand how to make it happen

Go to http://www.linux-mtd.infradead.org/
Get their sources (I got them from their annonymous CVS). There's more in
there than what is in the kernel.

Build mtd/drivers/mtd/devices/blkmtd.c and insert the resulting module,
providing the device= option to indicate the target CF/disk partition.

BUT!

You probably do not have as strong guarantees of reliability: jffs
journaling works directly on chips for which you know when the data has
effectively been written, but the ATA emulation of CFs hides that.

Also it is pretty slow: writes are not very fast, but more importantly,
mounting the fs takes long (I don't remember exactly... around one minute
for a 64MB partition IIRC). I found that problematic and went back to
ext2.

If we can't really have the same reliability anyway with CF, the remaining
important advantage is compression. But the jffs structure may not be all
that appropriate. Is there no other writable compressed filesystem
for linux anymore? All I found were old and well dead...

-- 
Stéphane Doyon
<s.doyon@videotron.ca>
http://pages.infinit.net/sdoyon/