Hello Volker


Read-only mounting prevents any writes to Yaffs, including any refresh.

It is true that NAND does have a read disturb issue were reading a page can cause corruption of bits on OTHER pages in the same block. However this typically takes many hundreds of thousands of read operations.

It is also possible that there is leakage with time.

The best way to assess the impact for your design is to discuss the read disturb prevalence with your NAND manufacturer.

Perhaps it would be good if Yaffs had a read-only mount mode that was read only except for doing refresh. Does that sound like something useful?


Regards

Charles




On Mon, Jan 29, 2018 at 10:48 PM, Volker Floeder <vf@floeder.com> wrote:
Ok, understood. Thanks!

However, all pages that are used by yaffs should be read when the file-system is mounted, correct?

So at least after a boot, there should be a read-access across all valid data. Or do I need some kind of "scrubbing" to be sure?


----- Ursprüngliche Mail -----
Von: "Bean Huo (beanhuo)" <beanhuo@micron.com>
An: vf@floeder.com
CC: yaffs@stoneboat.aleph1.co.uk
Gesendet: Montag, 29. Januar 2018 10:04:22
Betreff: RE: [Yaffs] Read-Only mounted YAFFS2 - refreshing of NAND pages

>
>Hi,
>
>I am wondering if the page-refresh works on a read-only mounted filesystem
>as well. However, if it would not, then some flash blocks might get
>uncorrectable read-errors after some period of time, so I'd expect that to
>work - but on the other hand, it might be a bad idea to mount read-only at
>all ...
>
>Does anybody know? Thanks!
>
>- Volker
>
>

According to my understanding, if there is read action on this read-only mounted
Partition, page-refresh will work. Even for the read-write mounted filesystem, if no read action,
page-refresh doesn't work.
mtd layer will report bitflips to file system layer, rather than file system itself.

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