Which file system to use?

[Douglas Lopes Pereira]

Hi guys,

According to Martin's we should format our USB stick or SD card using
EXT2 file system. I was wondering if I can use UBIFS instead (I don't
see any reasons not use it) but first I would like to count on yours
expertise.

Is there any advantage on using EXT2 instead of UBIFS?

Is UBIFS more appropriate for flash memory like USB sticks and SD
cards? Will UBIFS balance IO operations to preserve my SD card (I
mean, will it write my files in all the 'extension' of my SD and not
in only one point)?

Hope to hear from you guys.
Thanks for your time.

Regards,
Douglas


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[debian.arm.nospam]

On Tue, Oct 13, 2009 at 08:57:08 -0300, Douglas Lopes Pereira wrote:

> Hi guys,
>
> According to Martin's we should format our USB stick or SD card using
> EXT2 file system. I was wondering if I can use UBIFS instead (I don't
> see any reasons not use it) but first I would like to count on yours
> expertise.
>
> Is there any advantage on using EXT2 instead of UBIFS?
>
> Is UBIFS more appropriate for flash memory like USB sticks and SD
> cards? Will UBIFS balance IO operations to preserve my SD card (I
> mean, will it write my files in all the 'extension' of my SD and not
> in only one point)?

Although I have no practical experience with either UBIFS or JFFS2, from
what I've read on
http://www.linux-mtd.infradead.org/doc/ubifs.html#L_raw_vs_ftl it would
appear impossible to use UBIFS on a regular USB or SD card drive, as they
have a hardware mapping layer that hides the NAND flash characteristics
behind a block level emulation layer.

So I guess sticking with EXT2 is sound advice. (Although I recall reading
 somewhere that some USB stick vendors were suspected of optimizing their
wear leveling algorithms for FAT filesystems)



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[wookey-4]

+++ Douglas Lopes Pereira [2009-10-13 08:57 -0300]:
> Hi guys,
>
> According to Martin's we should format our USB stick or SD card using
> EXT2 file system. I was wondering if I can use UBIFS instead (I don't
> see any reasons not use it) but first I would like to count on yours
> expertise.

Nope. Although we call them 'flash drives' they don't present a flash
(MTD) interface - they present a block interface.

UBIFS (and JFFS2 and YAFFS) all talk to MTD (flash) directly.
Filesystems like EXT2 talk to block devices.

This is all very unfortunate because you are dependent for the
flash-management aspect of this on the behaviour of the secret
controller inside the stick, which is often optimised for FAT (extra
replaceable blocks at the front of the device where the cluster table
lives) and thus may wearout faster if used with other filesystems.

I believe LOGFS is intended to be a flash filesystem which can be used for
USB block device 'flash'.

> Is there any advantage on using EXT2 instead of UBIFS?

It works. You might be able to get UBIFS on a USB stick but it won't
do any of the useful things it does because it can't see the actual
flash).

Wookey
--
Principal hats:  iEndian - Balloonboard - Toby Churchill - Emdebian
http://wookware.org/


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