clustering and replication

With vmware and virtualisation it seems common to have both a cluster setup (high availability) and then also replicate all systems from a production SAN to a DR SAN. As I am not a network tech I am a bit confused how and what each is protecting against.

Is the cluster setup in your production SAN to protect against certain types of failure, and the DR SAN to protect against different types of failure? Can you give a laymans guide to what kind of disasters the local cluster setup saves you from - and what the DR SAN replicated setup saves you from?

I wasnt sure if you can have an overly complex setup, whereby if production host XYZ goes down, does another host in the cluster kick in to save the day - or does the repliated server on the DR SAN kick in to save the day? I assume the cluster and replicated copy are designed for specific types of failure - but I wasnt sure what.
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pma111Asked:
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Andrew Hancock (VMware vExpert / EE MVE^2)Connect With a Mentor VMware and Virtualization ConsultantCommented:
With vmware and virtualisation it seems common to have both a cluster setup (high availability) and then also replicate all systems from a production SAN to a DR SAN. As I am not a network tech I am a bit confused how and what each is protecting against.

Clustering or HA (High Availability), is the ability to maintain UPTIME or Availability of Virtual Machines, so it protects VM availability, in the event of a Host Failure, VMs will be restart within 1-2mins of failure. - so VM Failure.

Replication is the ability to prevent against total failure of Hosts and SAN. OR Datacentre, outage, e.g. DC has been blown up.

Is the cluster setup in your production SAN to protect against certain types of failure, and the DR SAN to protect against different types of failure? Can you give a laymans guide to what kind of disasters the local cluster setup saves you from - and what the DR SAN replicated setup saves you from?

Cluster provides high availability of VMs, that's all it does.

DR SAN protects against Primary SAN, failure, which is a single point of failure.

I wasnt sure if you can have an overly complex setup, whereby if production host XYZ goes down, does another host in the cluster kick in to save the day - or does the repliated server on the DR SAN kick in to save the day? I assume the cluster and replicated copy are designed for specific types of failure - but I wasnt sure what.

HA, VMs would restart on another Host. If SAN failed, DR SAN would be used.

HA and Replication are different methods of Availability and maintaining uptime.
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