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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