Gluster users - Feb 2017 - detecting replication issues

Hi all,

I have a simple replicated volume with a replica count of 3. To ensure any
file changes (create/delete/modify) are replicated to all bricks, I have
this setting in my client configuration.

 volume gv0-replicate-0
    type cluster/replicate
    subvolumes gv0-client-0 gv0-client-1 gv0-client-2
end-volume

And that works as expected. My question is how one could detect if this was
not happening which could poise a severe problem with data consistency and
replication. For example, those settings could be omitted from the client
config and then the client will only write data to one brick and all kinds
of terrible things will start happening. I have not found a way the gluster
volume cli to detect when that kind of problem is occurring. For example
gluster volume heal <volname> info does not detect this problem.

Is there any programmatic way to detect when this problem is occurring?

Thanks,
Joe
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On 02/23/2017 11:12 PM, Joseph Lorenzini wrote:
> Hi all,
>
> I have a simple replicated volume with a replica count of 3. To ensure
> any file changes (create/delete/modify) are replicated to all bricks,
> I have this setting in my client configuration.
>
>  volume gv0-replicate-0
>     type cluster/replicate
>     subvolumes gv0-client-0 gv0-client-1 gv0-client-2
> end-volume
>
> And that works as expected. My question is how one could detect if
> this was not happening which could poise a severe problem with data
> consistency and replication. For example, those settings could be
> omitted from the client config and then the client will only write
> data to one brick and all kinds of terrible things will start
> happening. I have not found a way the gluster volume cli to detect
> when that kind of problem is occurring. For example gluster volume
> heal <volname> info does not detect this problem. 
>
> Is there any programmatic way to detect when this problem is occurring?
>
I couldn't understand how you will end up in this situation. There is
only one possibility (assuming there is no bug :) ), ie you changed the
client graph in a way that there is only one subvolume to replica server.

To check that the simply way is, there is a xlator called meta, which
provides meta data information through mount point, similiar to linux
proc file system. So you can check the active graph through meta and see
the number of subvolumes for replica xlator

for example : the directory   <mount
point>/.meta/graphs/active/<volname>-replicate-0/subvolumes will have
entries for each replica clients , so in your case you should see 3
directories.


Let me know if this helps.

Regards
Rafi KC

> Thanks,
> Joe
>
>
>
>
>
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> Gluster-users mailing list
> Gluster-users at gluster.org
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