What is myHA?
To put it very simple - myHA is a technology that eliminates a single point of failure and allows to keep your business data accessible even in the event of one of the servers dying.
How does it work?
To benefit from it you will need at least two servers with the same storage capacity. They will be configured to behave as one logical unit. When one of the servers dies for any reason the other one will take over all of its duties with minimal disruption to the end users.
Who needs it?
If you can live with several hours of not being able to access your business files than this is not for you. However if downtime means a major disruption to your business processes than this is a service that you will definitely be glad to have.