UBI partitioning in embedded device?

[Ricard Wanderlof]

On Mon, 18 Apr 2011, Artem Bityutskiy wrote:

> On Mon, 2011-04-18 at 14:53 +0200, Ricard Wanderlof wrote:
>> On Mon, 18 Apr 2011, Atlant Schmidt wrote:
>>
>>> Ricard:
>>>
>>> One advantage of moving critical data (such as calibration
>>> data) into its own partition is that because each partition
>>> would absolutely positively *NOT* share its PEBs (Physical
>>> Erase Blocks) with any other partition, data stored in
>>> those partitions would then be better-insulated from
>>> "disturb" effects (such as "program disturb" and "read
>>> disturb") caused by the reading and writing of other data.
>>>
>>> Generally, the "disturb" effects only take place within Flash pages and
>>> from one Flash page to another.
>>
>> But is it even possible to have an UBI volume less than one eraseblock in
>> size? Normally a UBI volume would be several eraseblocks, so there's no
>> chance of any eraseblocks being shared at any one time between different
>> UBI volumes.
>>
>> I've always thought that because UBI volumes are measured in
>> number-of-LEBs, that each volume in practice gets its own PEBs, even
>> though of course UBI can move them around in the flash if it wants to.
>
> That's right, minimum size is one LEB. Probably Atlant meant that UBI
> will move data around, so the same PEBs will be "shared", meaning that
> today your critical calibration data is in PEB 1, tomorrow PEB 1
> contains some random non-critical stuff.

True, but then UBI will move the data to another PEB before that which 
should be ok. Of course, moving critical data could be seen as risky, but 
the way nand flash development is going, leaving it in place without 
potentially re-writing it is also risky.

I think what I'm most worried about is some bug in UBI causing the 
critical data to be lost at some point. And as you said, some form of 
backup would definitely help.

/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