Re: NAND flash misery

Vladimir Vassilevsky wrote:
"David Brown" <david@xxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote in message
CF cards and other earlier flash devices are not that great at wear
levelling and bad block handling (that's one of the reasons for
flash-specific file systems like YAFS and JFFS2).

The actual erase block size in NAND flash is something like 32/64/128/256KB,
being bigger for the higher capacity devices. What it implies: any write
operation through the IDE interface is actually read - copy - erase -
modify - write at the controller level.

Not if the implementor of the controller firmware did his homework. If
that's the case, a 512-byte block write ends up as a 512-byte block
write at the flash device, at a new address, and the old address is just
marked as unusable. No read/erase/modify/write for every operation.
Garbage compaction happens a some time in the background.

Since this kitchen is hidden behind IDE, there is no point in
using YAFS or JFS or such.

Exactly. Although I heard some controller firmware used in consumer
flash disks optimizes based on the assumption that the file system at
the other end of the IDE or USB interface is FAT.

A disk cache with the blocks of 32k makes a lot of sense though.

Not more or less for a flash disk than any other disk.


Stefan

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