Re: RAMFS, CRAMFS and JFFS2(was Re: /linuxrc query)

David Woodhouse (dwmw2@infradead.org)
Fri, 23 Mar 2001 19:37:46 +0000 (GMT)


On Fri, 23 Mar 2001, Amit D Chaudhary wrote:

> Hi David,
>
> I did consider CRAMFS and JFFS2 when it was announced on the mtd list.
> Conserving flash over system ram is more relevant. Our reasons are below:
>
> RAMFS v/s CRAMFS
> 1. RAMFS is just more stable in terms of less complexity, less bugs reported
> over the time, etc.
> 2. RAMFS is a fairly robust filesystem and all features required as far as I can
> tell.

I'm not aware of any bugs being found in cramfs recently - unless you
wanted to use it on Alpha (or anything else where PAGE_SIZE != the
hard-coded 4096 in mkcramfs.c).

I wouldn't avoid it for those reasons - although if you're _really_ short
of flash space, the same argument applies as for JFFS2 - a single
compression stream (tar.gz) will be smaller than compressing individual
pages like JFFS2 and cramfs do.

> I might be wrong and hence would welcome any suggestions.

Given your stated constraints - you're very short of flash and don't care
too much about the RAM you use, you've may have made the same choice I
would have done.

Bearing in mind that you have to take into account the overhead of the
initrd which does the untarring - what's the total size of the initrd +
tarball on the flash, and what size would the corresponding cramfs be?

If you could fit your root filesystem into a cramfs on the flash, I'd do
that instead and use ramfs for the parts which need to be writeable.

-- 
dwmw2

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