git-annex/doc/copies.mdwn
Joey Hess 7189dfd77d git-annex (5.20131127) unstable; urgency=low
* webapp: Detect when upgrades are available, and upgrade if the user
    desires.
    (Only when git-annex is installed using the prebuilt binaries
    from git-annex upstream, not from eg Debian.)
  * assistant: Detect when the git-annex binary is modified or replaced,
    and either prompt the user to restart the program, or automatically
    restart it.
  * annex.autoupgrade configures both the above upgrade behaviors.
  * Added support for quvi 0.9. Slightly suboptimal due to limitations in its
    interface compared with the old version.
  * Bug fix: annex.version did not get set on automatic upgrade to v5 direct
    mode repo, so the upgrade was performed repeatedly, slowing commands down.
  * webapp: Fix bug that broke switching between local repositories
    that use the new guarded direct mode.
  * Android: Fix stripping of the git-annex binary.
  * Android: Make terminal app show git-annex version number.
  * Android: Re-enable XMPP support.
  * reinject: Allow to be used in direct mode.
  * Futher improvements to git repo repair. Has now been tested in tens
    of thousands of intentionally damaged repos, and successfully
    repaired them all.
  * Allow use of --unused in bare repository.

# imported from the archive
2013-11-27 18:41:44 -04:00

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Markdown

Annexed data is stored inside your git repository's `.git/annex` directory.
Some [[special_remotes]] can store annexed data elsewhere.
It's important that data not get lost by an ill-considered `git annex drop`
command. So, git-annex can be configured to try
to keep N copies of a file's content available across all repositories.
(Although [[untrusted_repositories|trust]] don't count toward this total.)
By default, N is 1; it is configured by annex.numcopies. This default
can be overridden on a per-file-type basis by the annex.numcopies
setting in `.gitattributes` files. The --numcopies switch allows
temporarily using a different value.
`git annex drop` attempts to check with other git remotes, to check that N
copies of the file exist. If enough repositories cannot be verified to have
it, it will retain the file content to avoid data loss. Note that
[[trusted_repositories|trust]] are not explicitly checked.
For example, consider three repositories: Server, Laptop, and USB. Both Server
and USB have a copy of a file, and N=1. If on Laptop, you `git annex get
$file`, this will transfer it from either Server or USB (depending on which
is available), and there are now 3 copies of the file.
Suppose you want to free up space on Laptop again, and you `git annex drop` the file
there. If USB is connected, or Server can be contacted, git-annex can check
that it still has a copy of the file, and the content is removed from
Laptop. But if USB is currently disconnected, and Server also cannot be
contacted, it can't verify that it is safe to drop the file, and will
refuse to do so.
With N=2, in order to drop the file content from Laptop, it would need access
to both USB and Server.
Note that different repositories can be configured with different values of
N. So just because Laptop has N=2, this does not prevent the number of
copies falling to 1, when USB and Server have N=1. To avoid this,
configure it in `.gitattributes`, which is shared between repositories
using git.