Nutanix intelligent software features include Block Awareness. A "block" represents a physical appliance. Nutanix refers to a “block” as the chassis which contains either one, two, or four "nodes". The reason for distributing roles and data across blocks is to ensure if a block fails or needs maintenance the system can continue to run without interruption.
Nutanix Block Awareness can be broken into a few key focus areas:
- Data (The VM data)
- Metadata (Cassandra)
- Configuration Data (Zookeeper)
Block Awareness is automatic (always-on) and requires a minimum of 3 blocks to be activated, otherwise node awareness will be defaulted to. The 3-block requirement is there to ensure quorum.
AOS 5.8 introduced support for erasure coding in a cluster where block awareness is enabled. In previous versions of AOS block awareness was lost when implementing erasure coding. Minimums for erasure coding support are 4 blocks in an RF2 cluster and 6 blocks in an RF3 cluster. Clusters with erasure coding that have less blocks than specified will not regain block awareness after upgrading to AOS 5.8.
Nutanix, ECP [HCI]/5.19, Ultimate
Block Failure Protection, Reads/Writes, Data Availability