Re: Install Yocto image and backup

[Alexander Dahl <ada@thorsis.com>]

Hei hei,

Am Montag, 2. November 2020, 10:16:58 CET schrieb Jupiter:
> Hi Alexander,
> 
> Thanks for your advice.
> 
> > In my opinion two things are common practice:
> > 
> > 1) Using a layer on top of raw NAND, like UBI/UBIFS nowadays, so bad
> > blocks
> > can be handled properly in a layer below your rootfs.
> 
> Yes, the UBI/UBIFS is used in NAND partitions, I guess you alluded
> there is no need use the backup, right?

If your kernel and rootfs partition is just one UBIFS in a bigger UBI volume, 
then no. Single bad blocks affecting the UBIFS partitions would be handled by 
the underlying UBI. You should however consider using ubihealthd or something 
similar to become aware of badblocks over time and handle them before it's too 
late and you can not boot from the rootfs anymore, especially if it is read 
only and not touched for writing in normal operation.

> > 2) Using an A/B scheme for updating and using a well tested framework for
> > that  (instead of self written shell scripts).  You don't need another
> > NAND chip for that, just multiple partitions.  You can still have your
> > kernel/rootfs read-only at runtime.
> If I do need to use a backup, it won't need another NAND chip, it will
> be another UBI/UBIFS partition. But I would like as simple as possible
> if no backup is a common practice.

I don't think backup is the right term here. Backup would be something you 
make based on a running system.

I just looked briefly over the documentation of RAUC [1]. This is no explicit 
recommendation, there are other update frameworks, but you can find a lot of 
ideas and concepts in there frequently used in the embedded world for updates.

Your original question implied you want some kind of redundancy, but never 
update kernel and root filesystem, right? That's rather unusual at least if 
your device is somehow connected to a network. So what I suggested was having 
two rootfs partitions. One is active and the device boots from it (A), and the 
other one acts as inactive (B). When you update, write the new rootfs to the 
inactive partition and then just switch over and boot B instead. You might add 
a third partition for recovery or factory reset. Only the active partition 
would be used in the running system and can still be readonly there.

Alex

[1] https://rauc.readthedocs.io/



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