When it comes to the operating system running on a server, HA often equates to
An ability to software-mirror critical volumes or partitions, for example, through HP’s MirrorDisk/UX or Windows Disk Administrator (though the latter is not normally seen much nor recommended for production systems)
A highly available file system that supports redundant file allocation tables or similar structures
An ability to apply changes or patches “on the fly” or in another manner that minimizes downtime
Protecting the NFS server, in the case of UNIX-based solutions, where the NFS server represents a single point of failure. Therefore, the UNIX OS must support a high-availability option like clustering the NFS server. ...