4.0.0 is a significant upgrade and rewrite.  It should be backward compatible with existing installations.

The release comprises three packages:

 - BackupPC-4.0.0alpha0.tar.gz: the usual BackupPC release tar ball.

 - BackupPC-XS-0.01.tar.gz: a perl XS module with C code that replaces several BackupPC perl libraries for improved performance.

 - rsync-bpc-3.0.9.0.tar.gz: a modified rsync that runs on the server that has a shim layer that interfaces directly to the BackupPC file system.

I'll also push BackupPC-XS-0.01.tar.gz to CPAN, and at some point I'll push the source to GitHub  (maybe next weekend; I'm starting a new job tomorrow).  Of course, the tar balls above contain all the source too.

As you can guess from the release name, I do not recommend using this release in any production environment.  Having some people try it out in a sandbox in their environment would be very helpful.  One important area to test is upgrading an existing V3 installation, so it would be great to test not just a virgin V4 installation, but also to also first install V3, do some backups, then upgrade to V4.

The documentation is only partially updated.  I'm happy to answer questions - for example, there are some importact changes to the configuration settings. If you reply to this thread please only copy the backuppc-devel list.

I've pasted a short summary of features and changes.  More is in the documentation.

Craig

 - No use of hardlinks (except temporarily to do atomic renames).  Reference counting

   is handled at the application level.

 - Backups are stored as "reverse deltas" - the most recent backup is always filled

   and older backups are reconstitued by merging all the deltas starting with the

   nearest future filled backup and working backwards.

   This is the opposite of V3 where incrementals are stored as "forward deltas"

   to a prior backup (typically the last full backup or prior lower-level

   incremental backup, or the last full in the case of rsync).

 - Since the most recent backup is filled, viewing/restoring that backup (which is

   the most common backup used) doesn't require mergning any deltas from other backups.

 - The concepts of incr/full backups and unfilled/filled storage are decoupled.

 - Uses full-file MD5 digests, which are stored in the directory attrib files.

   Each backup directory only contains an attrib file.

 - The Pool layout still support chains to handle md5 collisions.  While collisions

   can be constructed and are now well-known, they are highly unlikely in the wild.

   Pool files are never renamed or moved, unlike V3.

 - Any backup can be deleted (deltas are merged into next older backup if it is

   not filled).

 - The reverse deltas allow "infinte incrementals" - no need for a full backup

   if you are willing to trade speed for the risk that a file change will

   not be detected if the mtime or size don't change.

 - An rsync "full" backup now uses --checksum (instead of --ignore-times),

   which is much more efficient on the server side - the server just needs to

   check the full-file checksum computed by the client, together with the mtime,

   nlinks, size attributes, to see if the file has changed.  If you want a more

   conservative approach, you can change it back to --ignore-times, which

   requires the server to send block checksums to the client.

 - The use of rsync --checksum allows BackupPC to guess a potential match

   anywhere in the pool, even on a first-time backup.  In that case, the usual

   rsync block checksums are still exchanged to make sure the complete file

   is identical.

 - Uses rsync-3.0.9 on the server side (in place of File::RsyncP), with

   a C code layer to interface to the BackupPC storage.  So the whole data

   path for rsync is now in compiled C code, which is generally faster than perl

   (other than compression, which is the same code in either case, and I/O).

 - Due to the use of rsync-3.X, acls and xattrs are supported, and other

   useful options (but not all) are supported.  Rsync protocol 30 supports

   the efficient incremental file list, which significantly improves memory

   usage and startup time.  It also supports MD5 full-file checksums, which

   match BackupPC's new digest.  That allows a full-file digest to be checked

   as easily as an mtime on the server side.

 - Significant portions of the BackupPC code are now compiled C code in a

   new module called BackupPC::XS that is dynamically linked to perl.

 - FTP Xfer method isn't supported yet.