"FS over BLOCKDEV over FLASH" versus "FS over FLASH"

Diego Roig diego.roig at grupoclave.com
Wed Dec 15 11:43:47 EST 1999

	There are two posibilities for implementing a filesystem over a
flash device (DiskOnChip or others).
	One, is implementing a block device emulation layer over flash, and
then a filesystem over it. The block device emulation layer can be a wear
leveliong one (like M'Systems NFTL) or one that just maps flash memory like
linear contiguous sectors. The filesystem over the block device needs to
have a journal or to be log structured to be inmune to power failures and
	The other apporoach, is implementing a filesystem over flash
	What I don´t understand, is what is the difference between layering
the filesystem over the block device and directly over flash ? The "block
device" layer, isn´t just an abstraction for some REAL device that adapts
well to the concept of contiguous sectors? Doesn´t flash memory adapt to
that concept?
	What are the drawbacks of implementing a standard log structured
filesystem over a block device abstraction of the flash that doesn´t
implement wear leveling?

Diego Roig Seigneur
Gerencia de Desarrollo
Research & Development
Clave Electrónica SA
Mail Address:
Salguero 2493
(B1650BTG) San Martín
Tel: +54-11-4755-4554
Fax: +54-11-4753-3265
mailto:diego.roig at grupoclave.com
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