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

[Pranith Kumar Karampuri]

On 03/09/2016 10:40 AM, Kaushal M wrote:
> On Tue, Mar 8, 2016 at 11:58 PM, Atin Mukherjee <amukherj at redhat.com> wrote:
>>
>> On 03/08/2016 07:32 PM, Pranith Kumar Karampuri wrote:
>>> 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.
>> Is this acceptable? If I have a,b,c sub directories in the volume and if
>> I mount the same volume in /mnt then do you mean to say I won't be able
>> to access /mnt/a or /mnt/b and I can only access them using sub
>> directory mounts? Or you are talking about some specific case here?
>>> 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.
> We use hardlinks to the `.glusterfs` directory on bricks. So wouldn't
> having multiple filesystems inside a brick break the brick?

You are right. I think we will have to do full separation, where it will 
be more like multiple tenants :-/.

>
> Also, I'd prefer if sub-directory mounts and sub-directory snapshots
> remained separate, and not tied with each other. This mail gives the
> feeling that they will be tied together.

With the above point, I don't think it will be.

>
>>> Pranith
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