[Gluster-users] Question on replicated volumes with bricks on the same server

[Paul Cuzner]

Hi Antonio, 

There's also a Fred's project on gluster forge, that shows you the brick relationships too 

https://forge.gluster.org/lsgvt 

To give you an idea, here's an example 

[root at rhs1-1 bin]# lsgvt.py 
Topology for volume myvol: 
Distribute set 
│ 
├──── Replica set 0 
│ │ 
│ ├──── Brick 0: rhs1-1:/gluster/brick1 
│ │ 
│ └──── Brick 1: rhs1-3:/gluster/brick1 
│ 
└──── Replica set 1 
│ 
├──── Brick 0: rhs1-2:/gluster/brick1 
│ 
└──── Brick 1: rhs1-4:/gluster/bric k1 

Cheers, 
Paul C 

----- Original Message -----

> From: "Vijay Bellur" <vbellur at redhat.com>
> To: "Antonio Messina" <antonio.s.messina at gmail.com>,
> gluster-users at gluster.org
> Sent: Wednesday, 12 February, 2014 11:21:50 PM
> Subject: Re: [Gluster-users] Question on replicated volumes with bricks on
> the same server

> On 02/11/2014 03:21 PM, Antonio Messina wrote:
> > Hi all,
> >
> > I would like to know how gluster distribute the data when two bricks
> > of the same volumes are on the same server. Specifically, I would like
> > to know if there is any way to spread the replicas on different nodes
> > whenever possible, in order not to lose any data if the node goes
> > down.
> >
> > I did a simple test and it seems that the way replicas are spread over
> > the bricks is related to the way the volume is created, that is if I
> > create a volume with:
> >
> > gluster volume create vol1 replica 2\
> > gluster-data001:/srv/gluster/vol1.1 \
> > gluster-data001:/srv/gluster/vol1.2 \
> > gluster-data002:/srv/gluster/vol1.1 \
> > gluster-data002:/srv/gluster/vol1.2
> >
> > replicas of a file will be stored on the two bricks of the same
> > server, while if I create the volume with
> >
> > gluster volume create vol1 replica 2\
> > gluster-data001:/srv/gluster/vol1.1 \
> > gluster-data002:/srv/gluster/vol1.1 \
> > gluster-data001:/srv/gluster/vol1.2 \
> > gluster-data002:/srv/gluster/vol1.2
> >
> > replicas will be saved on two bricks of different servers.
> >
> > So, my guess is that if I create a "replica N" replicated+distributed
> > volumes using the bricks:
> >
> > gluster-1:/srv/gluster
> > ...
> > gluster-[N*M]:/srv/gluster
> >
> > gluster internally creates a distributed volumes made of the following
> > replicated "volumes":
> >
> > replicated volume 1: gluster-[1..N]:/srv/gluster
> > replicated volume 2: gluster-[N+1..2N]:/srv/gluster
> > ...
> > replicated volume M: gluster-[N*(M-1)+1..N*M]:/srv/gluster
> >
> > Is that correct or there is a more complex algorithm involved?
> >

> The interpretation is correct. The way replica sets are chosen is
> related to the order in which bricks are defined at the time of volume
> creation.

> -Vijay

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