[Gluster-devel] use-case for 4 replicas and 1 arbiter

[Niels de Vos]

Hi Ravi,

Last week I was in a discussion about 4-way replication and one arbiter
(5 bricks per set). It seems that it is not possible to create this
configuration through the CLI. What would it take to make this
available?

The idea is to get a high available storage, split over three
datacenters. Two large datacenter have red and blue racks (separated
power supplies, networking etc.) and the smaller datacenter can host the
arbiter brick.

    .--------------------------.   .--------------------------.
    |           DC-1           |   |           DC-2           |
    | .---red---.  .--blue---. |   | .---red---.  .--blue---. |
    | |         |  |         | |   | |         |  |         | |
    | |         |  |         | |   | |         |  |         | |
    | |  [b-1]  |  |  [b-2]  | |===| |  [b-3]  |  |  [b-4]  | |
    | |         |  |         | |   | |         |  |         | |
    | |         |  |         | |   | |         |  |         | |
    | '---------'  '---------' |   | '---------'  '---------' |
    '--------------------------'   '--------------------------'
                           \           /
                            \         /
                             \       /
                          .-------------.
                          |     DC-3    |
                          | .---------. |
                          | |         | |
                          | |         | |
                          | |  [a-1]  | |
                          | |         | |
                          | |         | |
                          | '---------' |
                          '-------------'

Creating the volume looks like this, and errors out:

   # gluster volume create red-blue replica 5 arbiter 1 \
       dc1-red-svr1:/bricks/b-1 dc1-blue-svr1:/bricks/b-2 \
       dc2-red-svr1:/bricks/b-3 dc2-blue-svr1:/bricks/b-4 \
       dc3-svr1:/bricks/a-1
   For arbiter configuration, replica count must be 3 and arbiter count
   must be 1. The 3rd brick of the replica will be the arbiter

Possibly the thin-arbiter from https://review.gluster.org/19545 could be
a replacement for the 'full' arbiter. But that may require more time to
get stable than the current arbiter?

Thanks,
Niels