[Gluster-devel] Simplify creation and set-up of meta-volume (shared storage)

[Avra Sengupta]

With this option, the volume will be created and explicitly mounted on 
all the nodes, which are currently a part of the cluster. Please note 
that new nodes added to the cluster will not have the meta volume 
mounted explicitly.

So in a case where the console tries to use the volume from a peer in 
the cluster, which was added after the option was set it will not have 
the mount available to it. Hence I feel its best that the console 
continues with the explicit mounting, and showing explicit warning 
during stop/remove-brick of the meta volume in console and allow the 
operations.

There is no other impact on the console, as far as this feature is 
concerned.

Regards,
Avra

On 05/18/2015 09:27 AM, Shubhendu Tripathi wrote:
> Avra,
>
> We are planning to provide mounting of meta volume on the nodes of the 
> cluster from Console as part of volume syncing and addition of new 
> nodes to the cluster. Looks like if this option is set, the explicit 
> mounting of the meta volume from console is not required and it would 
> be taken care by gluster.
>
> Currently we show explicit warning during stop/remove-brick of the 
> meta volume in console and allow the operations. I dont feel there 
> would be any impact due to new feature.
>
> Kindly let us know if any other impact on console or we need to take 
> care of anything else as result of this feature.
>
> Thanks and Regards,
> Shubhendu
>
> On 05/15/2015 07:30 PM, Avra Sengupta wrote:
>> Hi,
>>
>> A shared storage meta-volume is currently being used by 
>> snapshot-scheduler, geo-replication, and nfs-ganesha. In order to 
>> simplify the creation and set-up of the same, we are introducing a 
>> global volume set option(cluster.enable-shared-storage).
>>
>> On enabling this option, the system analyzes the number of peers in 
>> the cluster, which are currently connected, and chooses three such 
>> peers(including the node the command is issued from). From these 
>> peers a volume(gluster_shared_storage) is created. Depending on the 
>> number of peers available the volume is either a replica 3 volume(if 
>> there are 3 connected peers), a replica 2 volume(if there are 2 
>> connected peers), or a single brick volume(if there is only one node 
>> in the cluster). "/var/run/gluster/ss_brick" serves as the brick path 
>> on each node for the shared storage volume. We also mount the shared 
>> storage at "/var/run/gluster/shared_storage" on all the nodes in the 
>> cluster as part of enabling this option.
>>
>> Once the volume is created, and mounted the maintainance of the 
>> volume like adding-bricks, removing bricks etc., is expected to be 
>> the onus of the user.
>>
>> On disabling the option, we provide the user a warning, and on 
>> affirmation from the user we stop the shared storage volume, and 
>> unmount it from all the nodes in the cluster.
>>
>> These are achieved with hook-scripts as part of the volume set 
>> option. If anyone is interested in having a look at the patch, it's 
>> available for review at http://review.gluster.org/#/c/10793/ . If 
>> there is any feedback and suggestion regarding the same, please feel 
>> free to share it.
>>
>> Regards,
>> Avra
>>
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>