More capacity or higher availability. That is the Hyperflex Replication Factor Question.
Hyperflex Replication Factor ?
A replication factor (RF) is the number of copies that the Hyperflex system writes the storage block. There are two options : A RF of 2 or a RF of 3. The default setting during installation of the Hyperflex system is 3. All the blocks are written with an algorithm so that none of the blocks are written on the same node or same disk. This eliminates the Single Point of Failure.
Once you choose your replication factor during the installation, you can not change it back ! You will have to do a complete re-installation of the system. But why would you choose a RF of 2 or 3 ?
Replication Factor 3 :
Due to the fact that there are more copies of the storage block on the Hyperflex system, the data integrity is higher. You can loose 2 nodes at the same time and the system still runs smoothly. There is a nice post on : Testing Cisco Hyperflex Auto Healing.
Replication Factor 2 :
If you got a development environment or you have a good backupsystem in place, you can think about choosing for the Replication Factor of 2. There are only 2 blocks on the system, so you can have only one node failure simultaneously. There is one big advantage when you choose RF2. Because there are less duplicated blocks on the system, you will have more storage available. The formula can be found at : Cisco Hyperflex Sizing Tool With a RF of 2, you can say that 50% of your raw capacity is usable.