Where is the "scrubbing" threshold set in UBI? Can it be easily varied?

[Artem Bityutskiy]

On Thu, 2014-07-03 at 10:07 -0400, Atlant Schmidt wrote:
> Folks:
> 
>   Within the UBI layer, where is the threshold set that
>   determines how many bit-flips must occur on a read
>   before the block is "scrubbed" (stored into another
>   location)?

Are you now talking about the MTD layer, and the amount of bits
corrected by an ECC? In that case, see what Pekon answered. There is a
configurable threshold and MTD won't tell UBI that there were bit-flips
unless the amount of bits corrected in an ECC "step" is greater or
equivalent to the threshold. This is documented.

>   And is this done on a page-by-page basis or on a
>   whole-LEB/PEB basis?

On the MTD/NAND driver level, there is a notion of ECC step. One NAND
page may consist of a single or multiple ECC steps...

UBI has no idea about ECC steps, though. It just schedules a PEB for
scrubbing if it gets -EUNCLEAN from MTD when it reads the PEB.

>  That is, if a single page has
>   more than threshold number of bit flips, will just
>   that page be relocated or will the entire LEB be
>   relocated to another PEB? 

Entire PEB will be copied to another PEB, and the LEB will be re-mapped
from the old PEB to the new PEB, and the old PEB will be erased.

-- 
Best Regards,
Artem Bityutskiy