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From "Jens Rantil" <>
Subject Heterogenous cluster and vnodes
Date Fri, 29 Aug 2014 14:09:39 GMT

I have a few of VM host (bare metal) machines with varying amounts of free hard drive space
on them. For simplicity let’s say I have three machine like so:
 * Machine 1
  - Harddrive 1: 150 GB available.
 * Machine 2:
  - Harddrive 1: 150 GB available.
  - Harddrive 2: 150 GB available.
 * Machine 3.
  - Harddrive 1: 150 GB available.

I am setting up a Cassandra cluster between them and as I see it I have two options:

1. I set up one Cassandra node/VM per bare metal machine. I assign all free hard drive space
to each Cassandra node and I balance the cluster using vnodes proportionally to the amount
of free hard drive space (CPU/RAM is not going to be a bottle neck here).

2. I set up four VMs, each running a Cassandra node with equal amount of hard drive space
and equal amount of vnodes. Machine 2 runs two VMs.

General question: Is any of these preferable to the other? I understand 1) yields lower high-availability
(since nodes are on the same hardware).

Question about alternative 1: With varying vnodes, can I always be sure that replicas are
never put on the same virtual machine? Or is varying vnodes really only useful/recommended
when migrating from machines with varying hardware (like mentioned in [1])?


Jens Rantil
Backend engineer
Tink AB

Phone: +46 708 84 18 32

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