Host and Storage Network Failures

Failure Scenario	Failure Behavior
Single or multiple host failure	Applications can automatically failover to other hosts in the same site or other hosts in the other site connected to the other array. This is driven by VMware HA assuming clusters are stretched between sites.
Stretched SAN fabric outage (FC or iSCSI) (failure of SAN interconnect between sites)	Host IO automatically continues on local paths in the local site. Uniformly connected hosts: experience some storage path failures for paths to the remote array and continue IO on paths to the local array. in each site will maintain access to local volumes with no more than a pause in IO. Non-uniformly connected hosts: do not have a SAN interconnect between sites, so this scenario is not applicable.
SAN fabric outage in one site	Applications can automatically failover to hosts at the other site connected to the other array. This is driven by host cluster software assuming clusters are stretched between sites. VMware HA, Oracle RAC, SQL Cluster, etc. Uniformly connected hosts: in the site without the SAN outage, experience some storage path failures for paths to the remote array and continue IO on paths to the local array. in the site with the SAN outage, will experience total loss of access to volumes and applications must failover to the other site as mentioned above. Non-uniformly connected hosts: in the site without the SAN outage, will maintain access to local volumes. in the site with the SAN outage, will experience total loss of access to volumes and applications must failover to the other site as mentioned above.

Failure Scenario

Failure Behavior

Single or multiple host failure

Applications can automatically failover to other hosts in the same site or other hosts in the other site connected to the other array.

This is driven by VMware HA assuming clusters are stretched between sites.

Stretched SAN fabric outage (FC or iSCSI)

(failure of SAN interconnect between sites)

Host IO automatically continues on local paths in the local site.

Uniformly connected hosts:

experience some storage path failures for paths to the remote array and continue IO on paths to the local array.
in each site will maintain access to local volumes with no more than a pause in IO.

Non-uniformly connected hosts:

do not have a SAN interconnect between sites, so this scenario is not applicable.

SAN fabric outage in one site

Applications can automatically failover to hosts at the other site connected to the other array.

This is driven by host cluster software assuming clusters are stretched between sites. VMware HA, Oracle RAC, SQL Cluster, etc.

Uniformly connected hosts:

in the site without the SAN outage, experience some storage path failures for paths to the remote array and continue IO on paths to the local array.
in the site with the SAN outage, will experience total loss of access to volumes and applications must failover to the other site as mentioned above.

Non-uniformly connected hosts:

in the site without the SAN outage, will maintain access to local volumes.
in the site with the SAN outage, will experience total loss of access to volumes and applications must failover to the other site as mentioned above.

The next two sections will describe how ESXi hosts in a stretched cluster configuration respond to certain failures including:

Host failures—what happens to VMs running on a host when it fails?
Array failure—what happens when a FlashArray fails?

The focus will not be on why the array goes down, but instead if the array goes down, how do ESXi and vSphere HA react?