Vsan Fault Domains - Dell EMC VxRail Appliance Operation Manual

vSAN fault domains

vSAN uses fault domains to configure tolerance for rack and site failures. By default, a node is
considered a fault domain. vSAN spreads storage object components across fault domains.
Therefore, by default, vSAN spreads storage object components across nodes.
Consider an 8-node cluster spread across four server racks, with two nodes in each rack. If the
FTT is set to 1 and fault domains are not configured, vSAN might store both replicas of an
object on hosts in the same rack. If so, applications are exposed to rack-level failure. By
defining the nodes in each rack as a separate fault domain, the system can be protected from
rack-level failures.
The figure below shows an 8-node cluster spread across four physical racks with four separate
fault domains:
 Fault domain 1 (FD1) contains esxi-01 & esxi-02
 Fault domain 2 (FD2) contains esxi-03 & esxi-04
 Fault domain 3 (FD3) contains esxi-05 & esxi-06
 Fault domain 4 (FD4) contains esxi-07 & esxi-08
In this scenario, vSAN ensures that storage object components are stored on nodes in different
racks.
Figure 18. vSAN Fault Domains
When fault domains are configured, vSAN applies the storage policy to the entire domain,
instead of the individual hosts. vSAN adjusts the placement of storage object to make them
compliant with the storage policy.
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