Git-annex special remote for accessing (Remote) Indexed file Archives (RIA)

This git-annex special remote implementation is very similar to the directory special remote type built into git-annex. There are a few key differences that outline the use cases where one might consider using this one instead:

• (Optional) read-access to (compressed) 7z archives

  (Parts of) the keys stored in the remote can live in a 7z archive. These archives are indexed and support relatively fast random read access. This feature can be instrumental on HPC storage systems where strong quotas on filesystem inodes might be imposed on users. The entire key store of the remote can be put into an archive, re-using the exact same directory structure, and remains fully accessible while only using a handful of inodes, regardless of file number and size.

• (SSH-based remote) access to a configurable directory

  An SSH host name can be provided and all interaction with the remote will be performed via SSH. Moving from local to remote operations, or switching target paths can be done via a change to the configuration (even without having to touch a repository at all). This makes it easier to accommodate infrastructural changes, especially when dealing with large numbers of repositories.

• Multi-repository directory structure

  While each repository has its own associated key store directory tree, the key store directories of multiple repositories can be organized into a homogeneous archive directory structure. For DataLad datasets, their ID is used to define the location of a key store in an archive. For any other repository the annex remote UUID is taken. This feature further aids the handling of large numbers of repositories in a backup or data store use case, because locations are derived from repository properties rather than having to re-configure them explicitly.

Installation

Before you install this package, please make sure that you install a recent version of git-annex. This special remote requires at minimum git-annex version 6.20160511. Afterwards, install the latest version of ria-remote from PyPi:

# install from PyPi
pip install ria-remote

Use

A ria special remote is set up like any other "external"-type remote via the git-annex initremote command. There is a single additional required setting in contrast to the standard ones: base-path which determines the base directory where the special remote places its keys:

git annex initremote myremote \
    type=external encryption=none \
    externaltype=ria base-path=/tmp/basepath/here

Alternatively, the base-path can also be provided via a Git configuration variable by setting annex.ria-remote.<remote>.base-path (in this example annex.ria-remote.myremote.base-path).

The remote is now ready for use. Any directories will be created on demand. The key store for a repository will be located underneath the given base path, in a structure like this:

/tmp/basepath/here
└── 2e5
    └── 24934-a09e-11e9-8503-f0d5bf7b5561
        └── annex
            └── objects
                └── ff4
                    └── c57
                        └── MD5E-s4--ba1f2511fc30423bdbb183fe33f3dd0f
                            └── MD5E-s4--ba1f2511fc30423bdbb183fe33f3dd0f

where the first two levels represent a tree structure that can host key stores for any number of repositories, and the remaining level are identical to the organization of a bare Git repository with the annex object tree following the layout of a directory-type git-annex special remote. The directory names for the two top-most levels are build from the git-annex UUID for the special remote, or a DataLad dataset UUID, if available.

The special remote also supports SSH-based operation. To enable it, an additional host name argument has to be given:

git annex initremote myremote \
    type=external encryption=none \
    externaltype=ria base-path=/tmp/basepath/here \
    ssh-host=ria.example.com

This configuration will make the special remote use /tmp/basepath/here on ria.example.com. Any SSH-access customizations (user name, ports, etc.) have to be implemented via the standard SSH configuration mechanism, for example, by placing a snippet like this in $HOME/.ssh/config:

Host ria.example.com
  User mike
  Port 2222
  PreferredAuthentications publickey

There are additional configuration settings available:

• By default ria-remote will check the remote end's layout version by reading a ria-layout-version file at the top-level (base-path) as well as at the individual dataset directories. If the layout version isn't known it will set its mode to "read-only" and will reject to write anything to that store in order to not accidentally mix up different layouts. This behavior can be overwritten by setting annex.ria-remote.<name>.force-write to true.

• The remote end can indicate that any occurring exception shall be written to a log file. This can be helpful for debugging problems in a multi-user central storage scenario. For this to be used, the version recorded in the ria-layout-version file can be appended by |l ('l' for logging). If done at the top of the dataset tree, this will applied to all datasets. However, since such a log can potentially leak private information, this configuration can be ignored by any client by setting annex.ria-remote.<name>.ignore-remote-config. There is no independent server-side processing, and all actions are performed by the client-side special remote instance.

Support

All bugs, concerns and enhancement requests for this software can be submitted here: https://github.com/datalad/git-annex-ria-remote/issues