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This changes the behaviour of cloning from a repository on the
local machine, by defaulting to "-l" (use hardlinks to share
files under .git/objects) and making "-l" a no-op. A new
option, --no-hardlinks, is also added to cause file-level copy
of files under .git/objects while still avoiding the normal
"pack to pipe, then receive and index pack" network transfer
overhead. The old behaviour of local cloning without -l nor -s
is availble by specifying the source repository with the newly
introduced file:///path/to/repo.git/ syntax (i.e. "same as
network" cloning).
* With --no-hardlinks (i.e. have all .git/objects/ copied via
cpio) would not catch the source repository corruption, and
also risks corrupted recipient repository if an
alpha-particle hits memory cell while indexing and resolving
deltas. As long as the recipient is created uncorrupted, you
have a good back-up.
* same-as-network is expensive, but it would catch the breakage
of the source repository. It still risks corrupted recipient
repository due to hardware failure. As long as the recipient
is created uncorrupted, you have a good back-up.
* The new default on the same filesystem, as long as the source
repository is healthy, it is very likely that the recipient
would be, too. Also it is very cheap. You do not get any
back-up benefit, though.
None of the method is resilient against the source repository
corruption, so let's discount that from the comparison. Then
the difference with and without --no-hardlinks matters primarily
if you value the back-up benefit or not. If you want to use the
cloned repository as a back-up, then it is cheaper to do a clone
with --no-hardlinks and two git-fsck (source before clone,
recipient after clone) than same-as-network clone, especially as
you are likely to do a git-fsck on the recipient if you are so
paranoid anyway.
Which leads me to believe that being able to use file:/// is
probably a good idea, if only for testability, but probably of
little practical value. We default to hardlinked clone for
everyday use, and paranoids can use --no-hardlinks as a way to
make a back-up.
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Junio C Hamano
Brian Gernhardt
Alex Riesen