[Gluster-devel] sub-directory geo-replication, snapshot features

[Pranith Kumar Karampuri]

hi,
          Late last week I sent a solution for how to achieve 
subdirectory-mount support with access-controls 
(http://www.gluster.org/pipermail/gluster-devel/2016-March/048537.html). 
What follows here is a short description of how other features of 
gluster volumes are implemented for sub-directories.

Please note that the sub-directories are not allowed to be accessed by 
normal mounts i.e. top-level volume mounts. All access to the 
sub-directories goes only through sub-directory mounts.

1) Geo-replication:
The direction in which we are going is to allow geo-replicating just 
some sub-directories and not all of the volume based on options. When 
these options are set, server xlators populate extra information in the 
frames/xdata to write changelog for the fops coming from their 
sub-directory mounts. changelog xlator on seeing this will only 
geo-replicate the files/directories that are in the changelog. Thus only 
the sub-directories are geo-replicated. There is also a suggestion from 
Vijay and Aravinda to have separate domains for operations inside 
sub-directories for changelogs.

2) Sub-directory snapshots using lvm
Every time a sub-directory needs to be created, Our idea is that the 
admin needs to execute subvolume creation command which creates a mount 
to an empty snapshot at the given sub-directory name. All these 
directories can be modified in parallel and we can take individual 
snapshots of each of the directories. We will be providing a detailed 
list commands to do the same once they are fleshed out. At the moment 
these are the directions we are going to increase granularity from 
volume to subdirectory for the main features.

Pranith