KHB: A Filesystems reading list
Posted Aug 24, 2006 2:26 UTC (Thu) by wookey
In reply to: KHB: A Filesystems reading list
Parent article: KHB: A Filesystems reading list
Last time I checked jffs/yaffs can't be used on generic block devices, only on memory devices (or with some wrapper driver).
Yes. This is the case. It would be nice to have the robustness of log-strucutreed filesystems on flash devices accessed as block devices, but it's actually very difficult to achieve. The problem is that although USB sticks and SD/MMC cards and CF cards use flash, they hide it behind a controller which does who-knows-what behind the scenes in order to make it look enough like a disk that cameras can pretend it is a DOS FAT disk. The controllers remap blocks to retire bad blocks and (on the better ones) to avoid premature wear in the cluster tables at the start of the FAT format. But precisely because they do these things there is little benfit to using a filesystems like YAFFS/JFFS which knows about flash directly and does the right thing itself. You might as well just use something designed for disks.
So you can use YAFFS/JFFS on smartmedia and xD cards because they expose raw NAND flash, but not on all the others.
Various sorts of shims have been considered but the general consensus seems to be that it's not worth bothering with.
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