UBIFS question

[Martin Townsend]

Hi Richard,

Thanks for the reply.  rsync is the backup plan, I just wanted to rule
other options out first. The flash devices are going to subjected to a
fairly harsh environment and the idea of being able to fail over to a
backup docker container was appealing.

Which leads me to a couple of questions:
1) I need to simulate flash devices reading corrupted
pages/blocks/LEBs. Is there currently a way of doing this? if not
would it be possible to write something, say a kernel module to sit
above the NAND driver to do this.  I just want to see what effect
corruption has on a live system and how these errors manifest
themselves.

2) One thing I'm going to have to do is write a background thread to
monitor the status of the filesystem and try and detect corruption
before the system becomes unstable, is there any way to find out the
validity of the LEBs, ie checking their checksums.

Many Thanks,
Martin.



On Wed, Mar 16, 2016 at 11:12 PM, Richard Weinberger
<richard.weinberger at gmail.com> wrote:
> On Wed, Mar 16, 2016 at 10:54 AM, Martin Townsend
> <mtownsend1973 at gmail.com> wrote:
>> I have an board with a 512MB Raw NAND flash memory device and 4GB
>> Managed eMMC flash memory device.  I would like to take advantage of
>> this and maintain a root filesystem on each and keep them in sync so
>> upgrades will upgrade each filesystem.  I can then use one of them as
>> a redundant image that can be used to correct the primary one or fail
>> over on device failure.  I have UBIFS on the raw NAND flash and ext3
>> on the eMMC flash.  My first thought was can I create a mirror using
>> raid but after researching it looks like the linux SW raid, although
>> very flexible, only supports block devices which rules out UBIFS.  I
>> could see some mails about a block device layer for UBI but I seem to
>> remember that this was read only or had certain restrictions.
>>
>> Next I thought about maybe using Docker so I could switch between the
>> 2 filesystems but saw a mail that UBIFS doesn't support WHITEOUT
>> feature that docker would require from the underlying filesystem as it
>> uses union/overlay filesystems.
>>
>> Just wanted to check that these assumptions are correct and I haven't
>> missed something and also if anyone knows of another method I would be
>> very interested in hearing it.
>
> Yes, you cannot do RAID1 between MTD and block devices.
> And yes, overlayfs does not fully work these day on UBIFS but I'm working on it,
> at least it is on my TODO list and I have some patches on my disk..
>
> Why can't you just rsync between the filesystems?
>
> --
> Thanks,
> //richard