Re: Available space loss due to fragmentation?

[Richard Weinberger <richard.weinberger@xxxxxxxxx>]

On Wed, Jul 10, 2019 at 5:18 PM Ben Schroeder <klowd92@xxxxxxxxx> wrote:
> Thanks for the reply Richard.
> I just wanted to reiterate that i am using SPI NOR Flash, partitioned
> in an A/B scheme as so:

Hmmm.
Did you create the rootfs using mkfs.ubifs with a different
compression than used
by the kernel?

> I am not sure the garbage collector will improve the available space issue.
> Regardless of the UBI being mounted with sync option enabled or disabled,
> the issue persists. Even if i allow time for the background thread to run.
> The issue seems very problematic when considering the fact that i am
> downgrading the filesystem, patching files to be slightly smaller size
> than before,
> and i am still running out of disk space, regardless of how long i
> wait for garbage collection.
> On this regard, i will stick with your answer that it can be a serious
> challenge if all nodes are packed,
> and there is little available free space.

How full is the filesystem btw?

> Could you please clarify your answer regarding binary patching UBI Volumes:
> > Yes, you can alter a dynamic volume as you wish. But keep NAND odds on mind.
> > So you need to replace whole LEBs.
>
> It was my understanding that because UBI keeps tracks of bad blocks
> and erase counters,
> so that overwriting an existing and running UBI partition using a
> binary diff against a newer UBI partition,
> might cause loss of that metadata, or even corruption.

You need to operate on UBI level, not mtd.
You can open /dev/ubiX_Y and ask it to replace whole LEBs.
UBI will take care of erase-counters and stuff.

-- 
Thanks,
//richard

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