Re: Available space loss due to fragmentation?

[Ben Schroeder <klowd92@gmail.com>]

On Thu, Jul 11, 2019 at 1:16 PM Richard Weinberger
<richard.weinberger@gmail.com> wrote:
>
> On Wed, Jul 10, 2019 at 5:18 PM Ben Schroeder <klowd92@gmail.com> 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?
mkfs.ubifs -r /tmp/rootfs -m 1 -e 0xFF80 -c 1024 -o data.ubifs
(I believe standard compression is used, lzo?)
>
> > 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?
250kb free out of 22mb ~ Approxy 1% free

>
> > 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.

I see, thanks!

>
> --
> Thanks,
> //richard

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