I just want to mention that the "rack" in Cassandra don't need to match the physical rack. As long as each "rack" in Cassandra fails independent of each other, it is fine.

That means if you have 6 physical servers each in an unique physical rack and Cassandra RF=3, you can have any of the following configurations, and each of them makes sense and all of them will work correctly:

1. 6 racks in Cassandra, each contains only 1 server

2. 3 racks in Cassandra, each contains 2 servers

3. 1 rack in Cassandra, with all 6 servers in it

On 03/04/2023 16:14, Jeff Jirsa wrote:
As long as the number of racks is already at/above the number of nodes / replication factor, it's gonna be fine.

Where it tends to surprise people is if you have RF=3 and either 1 or 2 racks, and then you add a third, that third rack gets one copy of "all" of the data, so you often run out of disk space.

If you're already at 3 nodes / 3 racks / RF=3, you're already evenly distributed, the next (4th, 5th, 6th) racks will just be randomly assigned based on the random token allocation.

On Mon, Apr 3, 2023 at 8:12 AM David Tinker <david.tin...@gmail.com> wrote:

    I have a 3 node cluster using the GossipingPropertyFileSnitch and
    replication factor of 3. All nodes are leased hardware and more or
    less the same. The cassandra-rackdc.properties files look like this:

    (rack2 and rack3 for the other nodes)

    Now I need to expand the cluster. I was going to use rack4 for the
    next node, then rack5 and rack6 because the nodes are physically
    all on different racks. Elsewhere on this list someone mentioned
    that I should use rack1, rack2 and rack3 again.

    Why is that?


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