[Gluster-users] geo-replicated Master Master cluster

Zohair Raza engineerzuhairraza at gmail.com
Mon Nov 26 11:44:45 UTC 2012

Understand your point, by the time I also tried with NFS like clustering
but didn't help

There is master-master geo replication planned in 3.4

I think it is for the same purpose, has anyone got an idea on it?

Zohair Raza

On Mon, Nov 26, 2012 at 2:58 PM, Robert Hajime Lanning
<lanning at lanning.cc>wrote:

> On 11/25/12 23:26, Zohair Raza wrote:
>> Hi,
>> Thanks for reply,
>> Can you please elaborate more on the last line, I understand that read
>> will have no issues. I tried implementing a replicated volume but the
>> problem is gluster starts uploading the file to node2 while copying for
>> example if I have a 500MB file in site1 which is being copied from a LAN
>> machine to node1 copies at the speed of my internet link which I want to
>> get copied at much faster speed (in MBps) as it is LAN.
>> Isn't there any way by which I can set synchronization speed or set
>> gluster to sync after the file is copied?
> All the smarts are in the client.
> If you have a replica count of 2, then when a client is writing, it is
> writing to 2 bricks at the same time.  There is no such thing as queuing
> for later sync.
> What happens if a client at site A is writing to the same file as a client
> at site B?  If you have a delayed write to a remote site, how do you solve
> write conflicts?  You would need to completely understand the file format
> and it's transactional state, so that the 2 separate writes can be merged
> without corrupting the file.
> If there is a conflict, there is no way to notify the process that was
> writing, because the write would have already returned as successful, since
> it was queued for later execution on the file.
> The only way to solve this, is to have synchronized locks and synchronized
> writes.  It needs to behave like a local filesystem with 2 processes
> writing.
> Geo-replication solves this by saying one site is the master and all
> writes happen there.  The other site is a replica of the master, period.
>  This gives you a single source of truth about file state and no conflicts
> to mediate.
> For a database with ACID transactions and atomic data structures, you can
> design the data and data structures for multi-master replication. You can
> state that the latest update of an atomic structure wins, then design your
> application around that.  For a filesystem, you can't, as you do not have
> visibility into the structure of the files.
> The commercial NAS systems that have multi-master capabilities, do it at
> the block level (not file) and do it synchronously.
> I currently do not know of a way to implement a multi-master asynchronous
> network filesystem, without introducing the possibility of file corruption.
> --
> Mr. Flibble
> King of the Potato People
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