RE: Unstable bits and JFFS2

Ricard Wanderlof
2012-04-14T04:21:28Z

On Fri, 13 Apr 2012, Artem Bityutskiy wrote:

> On Fri, 2012-04-13 at 12:40 -0400, Atlant Schmidt wrote:
>>
>> Unfortunately, ECC can only fix those PEBs that
>> are actually read. If one of the PEBs in your
>> filesystem is being used entirely to contain
>> obscure data that only gets read once in a
>> blue moon (i.e., very rarely), then multiple
>> read-/write-disturbs can hit accumulate in
>> that PEB and when it is finally read, it may
>> already contains too many errors to be
>> corrected by the ECC.
>>
>> We've seen this exact scenario occur with the
>> current UBI/UBIfs and will be implementing a
>> userland "scrubbing" system to ensure that
>> every PEB gets read at least once in a while
>> (e.g., weekly or whatever interval seems right).
>
> This is right, people should have a user-space app which periodically
> reads all /dev/ubiX_Y. Care to send a patch against mtd-www with some
> explantion of this issue and extend the unstable bits issue?

Would it not be preferable to have this functionality within UBI itself,
so that, for instance governed by some sysfs parameter, UBI reads through
all PEBs at some interval, triggering scrubbing of any blocks that require
too much ECC for comfort?

To me it seems something that userspace should not be concerned with,
given the rest of the features that UBI deals with so that userspace does
not have to.

/Ricard
--
Ricard Wolf Wanderlöf ricardw(at)axis.com
Axis Communications AB, Lund, Sweden www.axis.com
Phone +46 46 272 2016 Fax +46 46 13 61 30