Client vs Server Quorum

[Lindsay Mathieson <lindsay.mathieson@xxxxxxxxx>]

I'm unclear as to the distinction between the two, but my guess:

- Quorum is only relevant to replica volumes

- It is p[referable to have a odd number of replicas and a minimum of 3

Client Quorum;

- Client is the fuse client or gfapi driver

- Quorum check is performed by the client

- if the check fails, the client will fail writes
   * is there a timeout involved or does it fail immediately?

- Quorum is determined by how many active bricks the client can see

  * As determined by quorum-type and/or quorum-count

- Bricks remain up

- Datastore remains up

Server Quorum:

- Server is the brick process (glusterd?)

- enabled with server-quorum-type=server

- Quorum check is performed by the server

- Quorum is determined by how many active bricks the server can see

- If quorum fails
  * brick is brought down
  * datastore remains up

In both cases bricks which remain part of a quorum can still be written to, whereas bricks which are isolated are readonly, or down altogether and will be healed once quorums returns. In theory this will prevent split brain problems.

Question:

- Which is better, server or client quorums?

- Can you safely enable both? recommended?

thanks,

--

Lindsay

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