[Linux-cluster] sparse-file clone breaks on GFS2

Gionatan Danti g.danti at assyoma.it
Sat Sep 19 21:07:03 UTC 2020

Il 2020-09-19 18:57 Pierre-Philipp Braun ha scritto:
> On 19.09.2020 14:14, Gionatan Danti wrote:
>> cp --sparse=never
> Hello neighbor (ciao from France).
> I am not sure what you mean, as there **was both** the original and
> the copied file sums in my message.

Sorry, I somewhat managed to miss them :|

> Anyhow, thank you and good idea about --sparse=never.  I applied the
> checksum multiple times -- at at each step -- just to make sure the
> results are consistent.
> cp --sparse=never dummy.ext4 dummy-never.ext4
> cp --sparse=auto dummy.ext4 dummy-auto.ext4
> cp --sparse=always dummy.ext4 dummy-clone.ext4
> And the sums always remain the same.  So I only print the output only
> once here below.
> ce2b843692051a2f4f81366f9680b675  dummy.ext4
> 33e84fdf0a328a64c4edd00342dd433d  dummy-never.ext4
> 33e84fdf0a328a64c4edd00342dd433d  dummy-auto.ext4
> 33e84fdf0a328a64c4edd00342dd433d  dummy-clone.ext4
> Although the GFS2 sparse-file is fine and usable as-is, it cannot be
> copied with `cp` nor packed with GNU tar, and it does not matter if
> our aim is to actually keep the sparse.
> I also attempted to copy a GFS2 sparse file to some EXT4 file-system.
> cp --sparse=always dummy.ext4 /root/dummy-clone-on-ext4.ext4
> And same happens.
> 33e84fdf0a328a64c4edd00342dd433d  /root/dummy-clone-on-ext4.ext4
> While with the inverse, namely copying an EXT4 sparse-file on GFS2.
> cd /root/
> dd if=/dev/zero of=dummy-on-ext4.ext4 bs=1G count=0 seek=1
> mkfs.ext4 dummy-on-ext4.ext4
> cp --sparse=always dummy-on-ext4.ext4 /data2/dummy-clone-from-ext4.ext4
> delivers the sparse-file intact.  No problem there.
> cd573cfaace07e7949bc0c46028904ff  /root/dummy-on-ext4.ext4
> cd573cfaace07e7949bc0c46028904ff  /data2/dummy-clone-from-ext4.ext4
> and... WOW!  Cloning it yet again, it finally remains intact!
> cd573cfaace07e7949bc0c46028904ff  dummy-clone-from-ext4-and-clone.ext4
> cd573cfaace07e7949bc0c46028904ff  dummy-clone-from-ext4.ext4
> It's strange.  Anyone?

Absolutely. Really strange.

> In case it matters, I am using vanilla Linux 4.18.20 and not the RHEL
> nor CentOS with patches.

What distribution are you using (Slackware)? Any additional data about 
your filesystem (ie: num journals/nodes)? I would like to try to 
replicate the issue if I can find some spare time...


Danti Gionatan
Supporto Tecnico
Assyoma S.r.l. - www.assyoma.it
email: g.danti at assyoma.it - info at assyoma.it
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