[Gluster-users] write-behind / write-back caching (asked again - nobody can help?)

Pavan T C tcp at gluster.com
Wed Aug 31 00:05:09 PDT 2011

On Tuesday 30 August 2011 08:36 PM, Christian wrote:
> Hello to all,
> I'm currently testing glusterfs ( version 3.1.4, 3.1.6, 3.2.2, 3.2.3 and
> 3.3beta ) for the following situation / behavior:
> I want to create a replicated storage via internet / wan with two
> storage nodes.
> The first node is located in office A and the other one is in office B.
> If I try to write a file to the mounted glusterfs (mounted via glusterfs
> or nfs), the write performance is as poor as the upload speed (~ 1 mbit
> - adjusted manually using "tc").
> I tested several cache-options (see below) with the following effect:
> The copy process of a file is done very fast (~40 mbyte/sec), but the
> application (rsync, mc copy, cp) is waiting at 100% for the final sync
> of the storage. The process is not finished before glusterfs has written
> the file to the 2nd node.

With a replicate config, this is what you can expect. The increased 
write-behind cache is holding your file giving you the boosted 
throughput, but on close, it will have to sync the data to both nodes.

> The behavior I am looking for is to store files locally first and then
> sync the content to the second node in the background.
> Is there a way for this?

I think you are better off using geo-replication rather than the 
traditional replicate configuration for the above requirement of yours.

The following link should help you configure geo-rep -


Look for the geo-replication section there. It also gives you a 
comparison of replicated volumes vs geo-replication.


> ******************************************************************
> volume info:
> Volume Name: gl5
> Type: Replicate
> Status: Started
> Number of Bricks: 2
> Transport-type: tcp
> Bricks:
> Brick1:
> Brick2:
> Options Reconfigured:
> nfs.disable: off
> nfs.trusted-sync: on
> nfs.trusted-write: on
> performance.flush-behind: off
> performance.write-behind-window-size: 200MB
> performance.cache-max-file-size: 200MB
> ******************************************************************
> tested mount options:
> mount.nfs /mnt/gluster/ -v -o mountproto=tcp -o async
> mount -t glusterfs /mnt/gluster -o async
> Thanks a lot,
> Christian
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