Re: CoW behavior when writing same content

[Roman Mamedov <rm@romanrm.net>]

On Tue, 9 Oct 2018 09:52:00 -0600
Chris Murphy <lists@colorremedies.com> wrote:

> You'll be left with three files. /big_file and root/big_file will
> share extents, and snapshot/big_file will have its own extents. You'd
> need to copy with --reflink for snapshot/big_file to have shared
> extents with /big_file - or deduplicate.

Or use rsync for copying, in the mode where it reads and checksums blocks of
both files, to copy only the non-matching portions.

rsync --inplace

              This  option  is  useful  for  transferring  large  files   with
              block-based  changes  or appended data, and also on systems that
              are disk bound, not network bound.  It  can  also  help  keep  a
              copy-on-write filesystem snapshot from diverging the entire con‐
              tents of a file that only has minor changes.

-- 
With respect,
Roman