Product : Cisco, HyperFlex [HCI]/4.0, x86
Feature : Disk Failure Protection, Reads/Writes, Data Availability
Content Owner:  Herman Rutten
Summary
1-2 Replicas (2N-3N)
Details
HyperFlexs implementation of replicas is called Replication Factor or RF in short (RF2 = 2N; RF3 = 3N). Maintaining 2 replicas (RF3) is the default method for protecting data that is written to the HyperFlex cluster. It applies to both disk and node failures. This means the HX storage platform can withstand a failure of any two disks or any two nodes within the storage cluster.

An Access Policy can be set to determine how the storage cluster should behave when a second failure occurs and effectively a single point of failure (SPoF) situation is reached:
- The storage cluster goes offline to protect the data.
- The storage cluster goes into read-only mode to facilitate data access.
- The storage cluster stays in read/write mode to facilitate data access as well as data mutations.

The self-healing process after a disk failure kicks in after 1 minute.

Replicas: Before any write is acknowledged to the host, it is synchronously replicated to the active Log on another node. All nodes in the cluster participate in replication. This means that with 3N one instance of data that is written is stored on one node and other instances of that data are stored on two different nodes in the cluster. For all instances this happens in a fully distributed manner, in other words, there is no dedicated partner node. When a disk fails, it is marked offline and data is read from another instance instead. At the same time data re-replication of the associated replicas is initiated in order to restore the desired Replication Factor.
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