ubifs: missing FAQ item regarding default compression options?

ubifs: missing FAQ item regarding default compression options?

[Daniel Drake]

Hi,

OLPC is looking more seriously at making the switch from jffs2 to
ubifs. We did this for a few months but we found that ubifs has
significantly higher (10-15%) disk space requirements for the same
data, compared with jffs2. We switched back to jffs2 because of this,
promising to look at ubifs again later (i.e. now).

What I didn't realise clearly at the time is that mkfs.jffs2 defaults
to zlib compression, and mkfs.ubifs defaults to LZO compression. So,
this was not a fair test. If I switch ubifs to zlib compression, it
produces results very similar to jffs.

For example, for one OS image, mkfs.jffs2 + sumtool produced a 664mb
file. mkfs.ubifs (with zlib selected) + ubinize created a 668mb image
of the same data - very comparable.

Should this be a FAQ entry? Others who aren't aware of this difference
in default compression options may run into the same non-issue.

Thanks,
Daniel

Re: ubifs: missing FAQ item regarding default compression options?

[Artem Bityutskiy]

On Sun, 2011-07-24 at 00:02 +0100, Daniel Drake wrote:
> Hi,
> 
> OLPC is looking more seriously at making the switch from jffs2 to
> ubifs. We did this for a few months but we found that ubifs has
> significantly higher (10-15%) disk space requirements for the same
> data, compared with jffs2. We switched back to jffs2 because of this,
> promising to look at ubifs again later (i.e. now).
> 
> What I didn't realise clearly at the time is that mkfs.jffs2 defaults
> to zlib compression, and mkfs.ubifs defaults to LZO compression. So,
> this was not a fair test. If I switch ubifs to zlib compression, it
> produces results very similar to jffs.
> 
> For example, for one OS image, mkfs.jffs2 + sumtool produced a 664mb
> file. mkfs.ubifs (with zlib selected) + ubinize created a 668mb image
> of the same data - very comparable.
> 
> Should this be a FAQ entry? Others who aren't aware of this difference
> in default compression options may run into the same non-issue.

Hi Daniel,

sure, send a patch against the mtd-www repo:

git://git.infradead.org/mtd-www.git

and add this piece of information. The web site is very simple and
you'll find out how to edit it easily. Then type "make" to build it.

-- 
Best Regards,
Artem Bityutskiy (Битюцкий Артём)