Re: UBIFS power cut issues

[JiSheng Zhang <jszhang3@gmail.com>]

Hi Artem,

2009/9/8 Artem Bityutskiy <dedekind1@gmail.com>:
> Hi,
>
> sorry for late answer, was very busy.
>
> On Wed, 2009-09-02 at 17:35 +0800, JiSheng Zhang wrote:
>> If we cut power when copy file into ubifs, then remount ubifs and try
>> to read the file, we found that the data at some offset of the file
>> began different from the data of the original file at the same offset.
>> Is this a bug of ubifs?
>
> This is expected behavior on any asynchronous FS. You may switch to
> synchronous behavior with '-o sync' mount option. I wrote a lot of

I have tested with "mount -o sync", the result is the same. It's not
empty file. For example:
cp fileA /mnt/ubifs/fileB
random cut power before "cp" completed.
then remount
>From head of /mnt/ubifs/fileB to some offset offsetC is the same as
fileA. But from offsetC to the end is different from fileA at the same
offset offsetC, it's not empty either.
Hope I expressed myself clearly.

> docs about write-back and the related issues. Dig UBIFS docs and FAQ.
> E.g.:
>
> http://www.linux-mtd.infradead.org/faq/ubifs.html#L_empty_file
> http://www.linux-mtd.infradead.org/doc/ubifs.html#L_writeback
>
> If you have a _specific_ question, feel free to ask, of course. But
> for this general question I do not have a better answer than RTFM
> :-)))
>
>> PS:how do you test data integrity of ubifs under power loss?
>
> We mostly checked it using either 'integck' (see mtd-utils) or
> 'fsstress' (see LTP). We ran those tests and cut power off at random
> points using these devices:
>
> http://www.cpscom.com/gprod/ipn.htm
>
> Then we mounted the FS. We did not really check the contents of the
> FS, because it is not simple and tricky, but we checked that it mounts,
> re-mounts, and files are readable/writable/deletable.

Thanks for this information.

Regards,
Jisheng