Re: Grow btrfs partition & filesystem backwards

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On Wednesday, 09 November, 2011 08:36:24 Chris Mason wrote:
> The only choice for an online operation is to make a new partition in
> front of the old one and just add that as a second disk in btrfs.
> 
> The slow method of shifting the bytes down is probably a better long
> term choice.
> 
> -chris

Hi Chris,

does the chunk tree be able to map the sectors "before" ? If so we should only 
"shift down" the map logical->physical in the chunk tree/device tree.

The only exception should be the superblock which has to be moved.

At the mount time we should pass a parameter which set how the data should be 
moved backward. Then the kernel remap the chunk tree/device tree.

I don't know if the gains is greater than the work, but from a theoretical 
point of view, it should be doable..



> 
> On Wed, Nov 09, 2011 at 06:40:06AM -0600, Billy Crook wrote:
> > I think the biggest point of contention is that with all the stuff
> > going on in the background in btrfs, its difficult to be sure that the
> > resize operation has completed.  With grows, you don't have to worry.
> > With shrinks, if you truncate the block device too soon, you will
> > corrupt the filesystem.
> > 
> > 2011/11/9 Ernst Sjöstrand <ernstp@xxxxxxxxx>:
> > > Gparted can do that, it just takes a very long time because it moves
> > > everything back first.
> > > 
> > > Regards
> > > //Ernst
> > > 
> > > On Wed, Nov 9, 2011 at 05:23, Jordan Windsor <jordanw2@xxxxxxxxx> wrote:
> > >> Hello,
> > >> I was wondering how I would go about growing a btrfs filesystem
> > >> backwards, I don't have any space to store the files temporally,
> > >> I'd
> > >> need to do it in place.
> > >> Thanks.
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