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UBIFS

UBIFS

Posted Apr 4, 2008 13:24 UTC (Fri) by NAR (subscriber, #1313)
Parent article: UBIFS

Are any of these filesystems supported on other operating systems? If I format an USB stick to
one of these filesystems, will the stick be readable from other operating systems?


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UBIFS

Posted Apr 4, 2008 17:31 UTC (Fri) by dedekind (guest, #32521) [Link]

This stuff is for embedded systems and it is not relevant for USB sticks and other FTL-enabled
things (with few weird exceptions probably).

UBIFS

Posted Apr 4, 2008 19:34 UTC (Fri) by Cato (subscriber, #7643) [Link]

No. Basically there are two types of flash devices, in simple terms:

1. Consumer flash devices - SD Cards, USB sticks, etc - these emulate hard drives by use of a
Flash Translation Layer (FTL) that hides any bad eraseblocks (flash blocks) and does 'wear
levelling' i.e. ensuring that no single flash block is used too much.  Flash blocks wear out
after 10K to 100K writes.  Different consumer flash devices have different FTLs, and writing a
good FTL is apparently hard.  Filesystems that work with such devices are all the normal Linux
hard drive ones - ext3, JFS, XFS, vfat - but they are wholly dependent on the FTL to work.

2. 'Raw' flash devices, aka Memory Technology Devices (MTDs).  These are key parts of consumer
flash devices, but aren't usable directly without an FTL, which is not included.  They expose
the differences between NOR and NAND flash (which are quite large).  MTDs require an
MTD-specific filesystem, e.g. YAFFS, JFFS2, LogFS, etc, and some of these FSs are specific to
NAND or NOR technology.

I've just been reading up on this so some of the above may be slightly off - it's a
complicated area.  The FAQs at http://www.linux-mtd.infradead.org/faq/general.html were quite
helpful, as were the LWN articles of course.

FTL in consumer flash devices

Posted Jul 24, 2008 18:05 UTC (Thu) by brouhaha (subscriber, #1698) [Link]

In the "consumer flash devices" you cite (SD cards, USB sticks), the FTL is entirely embedded and hidden inside the flash device itself. That's also true of MMC cards and CF cards. It was NOT true for so-called "SmartMedia", but that died a well-deserved death. I'm not sure about some other types such as Memory Stick and XD cards.
Filesystems that work with such devices are all the normal Linux hard drive ones - ext3, JFS, XFS, vfat - but they are wholly dependent on the FTL to work.
Acutually, the filesystems are wholly independent of the FTL. Brand X and Brand Y SD cards might have any entirely different FTL embedded in them, but ext3 doesn't know or care, because they present the same interface to the system.

FTL in consumer flash devices

Posted Jul 25, 2008 20:29 UTC (Fri) by nix (subscriber, #2304) [Link]

They're dependent on the FTL in the sense that if the FTL wasn't there, 
they'd ruin the card in short order. Their *code* is not dependent on the 
FTL, but their *proper functioning* is, exactly because they're not 
designed for Flash devices.


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