Re: Question on replicated volumes with bricks on the same server

[Paul Cuzner <pcuzner@xxxxxxxxxx>]

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@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/brick1

Cheers,

Paul C

---

From: "Vijay Bellur" <vbellur@xxxxxxxxxx>
To: "Antonio Messina" <antonio.s.messina@xxxxxxxxx>, gluster-users@xxxxxxxxxxx
Sent: Wednesday, 12 February, 2014 11:21:50 PM
Subject: Re: 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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