This special remote type stores file contents in a
[ddar](https://github.com/basak/ddar) repository. This provides easy
de-duplication when you use git-annex to manage many files that are similar.

Unlike bup, ddar uses its own storage format, which allows for both creation
and deletion of de-deduplicated files. In addition to using local storage, ddar
archives can be remote, providing that ddar is installed on the remote machine
and ssh is available to it.

See [[walkthrough/using_ddar]] for usage examples.

## encryption

Encryption is nominally supported, but is not useful. Since effective
encryption necessarily obfuscates file contents, similar areas across different
files are no longer visible to ddar and cannot be de-duplicated.

## compression

The same caveat with encryption also generally applies to compression, since
file compression changes file contents such that similar regions across files
no longer appear similar. An exception is `gzip --rsyncable`, which is
specifically designed to work around this issue. This is the only compression
mechanism with which de-duplication remains effective.

## configuration

These parameters can be passed to `git annex initremote` to configure ddar:

* `encryption` - One of "none", "hybrid", "shared", or "pubkey".
  See [[encryption]]. However, note that encryption renders all de-duplication
ineffective.

* `keyid` - Specifies the gpg key to use for [[encryption]].

* `ddarrepo` - Required. This is passed to `ddar` as the path to the ddar
  archive to use. If it doesn't exist, the ddar repository will be created
  automatically when a file is first copied to it. To use a remote ddar
  repository, use a colon (`:`) to separate the hostname from the remote path.
  Example: "ddarrepo=example.com:/big/myddar" or "ddarrepo=/big/myddar"