[Gluster-devel] Few details needed about *any* recent or upcoming feature

[Shyam]

Hi Niels,

Here is something for DHT2:

DHT2:

* Why DHT2:
To address consistency and correctness of operations, complexity and 
scale requirements in the gluster IO path, keeping performance 
characteristics unchanging.

The issue with current DHT is that a directory is present in all 
subvolumes of DHT, this leads to a few consistency issues when dealing 
with entry operations on directories or files. It also leads to scaling 
limitations when dealing with larger subvolume counts. Resolution of the 
consistency and correctness issues is becoming more complex and also 
involves some fine grained locking across the network, which would 
increase the complexity of the solution and also potentially decrease 
the performance of the file system.

Refer:
http://www.gluster.org/community/documentation/images/f/fd/Summit-dht2.odp

* Outline of approach:
To resolve some of the above inadequacies in the current DHT design, 
DHT2 aims to simplify the on disk data, and retain a directory in a 
single subvolume and hence address the various pitfalls that are present 
in the current distribution model.

It also addresses some of the other problems in DHT w.r.t layouts stored 
per directory and simplifies the same in order to retain consistency and 
correctness properties.

In the move to retain a directory on just a subvolume of DHT2, 
separation of namespace/inode and data becomes essential to make the 
distribution of data even. As a result DHT2, introduces a metadata 
sub-volumes and a data sub-volumes into gluster.

* Impacts:
- DHT2 changes the on disk format for gluster and hence does not provide 
an upgrade path from older DHT based volumes. It is not intended to in 
place convert older gluster volumes to newer gluster volumes as well.

- The on disk format changes also means changes to some other xlators 
like quota and possibly bit-rot and change log. Impact to these xlators 
are being analyzed

Shyam

On 01/20/2016 05:41 AM, Niels de Vos wrote:
> Hi all,
>
> on Saturday the 30th of January I am scheduled to give a presentation
> titled "Gluster roadmap, recent improvements and upcoming features":
>
>    https://fosdem.org/2016/schedule/event/gluster_roadmap/
>
> I would like to ask from all feature owners/developers to reply to this
> email with a short description and a few keywords about their features.
> My plan is to have at most one slide for each feature, so keep it short.
>
> Thanks,
> Niels
>
>
>
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