[clug] Kernel without initramfs

Daniel Pittman daniel at rimspace.net
Thu Mar 26 02:21:34 GMT 2009

Robert Edwards <bob at cs.anu.edu.au> writes:

> I notice in one of your earlier posts that you may be using ext3 on
> your CF device. May I suggest that it is a bad idea to use ext3 in
> particular and most other journalling FS's in general on a
> "flash"-based device?

You can suggest that, but you would be wrong, since one of your
underlying assumptions is incorrect.

> There are special FS's to use such as jffs, but I would recommend
> dividing up your file-system structure into read-only bits (eg. /usr)
> and writable parts.

JFFS will not work without significant contortions on a CompactFlash
device, as it requires direct access to the underlying flash hardware.

CF devices present as IDE, and have in-software wear levelling.

> For the writable parts work out if you can afford to write to a
> RAM-base FS and then copy important data back to non-volatile
> storage. Logging etc., if possible, should be to an external logging
> server.

That is generally good advice.

Anyway, to the specifics of your suggestion: the reason that ext3 is no
more likely to cause a CF card trouble than any other filesystem is
simple, and that is that the CF card performs wear levelling internally.

JFFS is designed for direct access to the flash hardware, in which there
is no hardware wear levelling, so it is essential to balance writes.

Also, notably, most CF hardware is used with a FAT filesystem on it.
That has an even hotter write area than ext3, in that the FAT data is
much more fixed in place...


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