Re: cross-subvolume cp --reflink

[Marc MERLIN <marc@merlins.org>]

On Thu, Aug 16, 2012 at 09:20:00PM -0700, james northrup wrote:
> dunno if this thread is dead, but im inclined to patch in cp --reflink
> to "fdupes" prog.  It  currently does provide a poor-man's dedupe via
> md5sum and hardlink, or delete.
> 
> all the better if the distro-kernels can backport cross-snapshot
> reflinks sooner than later.
 
So, I'd love for cp --reflink to bring back a deleted VM (huge file) from a
snapshot back to trunk without duplicating it.
But how would fdupes help? I can't hardlink between two snapshots, can I?

gandalfthegreat:/mnt/btrfs_pool1# ln usr_weekly_20120812_00\:02\:01/svn-commit.tmp  usr/test
ln: failed to create hard link `usr/test' => `usr_weekly_20120812_00:02:01/svn-commit.tmp': Invalid cross-device link

So, is there anything user space can do without kernel support?

Marc

> On Sun, Apr 29, 2012 at 1:05 PM, Norbert Scheibner <scno@gmx.net> wrote:
> > Am 29.04.2012, 01:53 Uhr, schrieb Hubert Kario <hka@qbs.com.pl>:
> >
> >
> >> On Sunday 01 of April 2012 11:42:23 Jérôme Poulin wrote:
> >>>
> >>> On Sun, Apr 1, 2012 at 11:27 AM, Norbert Scheibner <scno@gmx.net> wrote:
> >>> > Some users tested this patch successfully for week,s or months in 2 or
> >>> > 3
> >>> > kernel versions since then, true?
> >>> If this feature must be implented in VFS in another patch, why not
> >>> just activate what works and make the future patch disable it again?
> >>
> >>
> >> Why would (should) it be impleemented in VFS? reflink copy is completely
> >> different from normal copy and hard link.
> >
> >
> > I wouldn't make a VFS issue out of that. That should be another discussion.
> >
> > But:
> >
> >> Subvolumes in btrfs are barriers *only* in btrfs and not visible in VFS.
> >
> >
> > That is just a bug in my opinion, so it should work anyway, but to look at
> > it from VFS point of view is strengthening me in wanting the outstanding
> > patches integrated, as this feature could be supported by VFS in the future.
> >
> >
> >> IMHO it's strictly btrfs business and not supporting reflink copy between
> >> arbitrary directories is a bug.
> >
> >
> > I don't know exactly, but I think ZFS is another candidate for "cp
> > --reflink". For some of the log-structured filesystems this could be usefull
> > too, but I don't know if some of them already supports this or plan to
> > support this in the future.
> >
> > Greetings
> >     Norbert
> >
> > --
> > To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
> > the body of a message to majordomo@vger.kernel.org
> > More majordomo info at  http://vger.kernel.org/majordomo-info.html
> --
> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

-- 
"A mouse is a device used to point at the xterm you want to type in" - A.S.R.
Microsoft is to operating systems ....
                                      .... what McDonalds is to gourmet cooking
Home page: http://marc.merlins.org/