Compared to general purpose machines, a filer requires dramatically fewer commands to manage all of its functions. Disks of various capacities can be mixed within the RAID array. The file system is a single expandable partition - just add a disk to increase file system capacity. This degree of simplicity is just not possible with a general- purpose server. Finally, the appliance-modeled filer is more reliable.
Software is the primary culprit of downtime among traditional file servers.
The filer on the other hand, contains less code than any general-purpose device. This means it is easily tested and supported. With integrated RAID, the filer delivers data safety and high availability. Disk failure does not result in system downtime. For all their advantages, however, appliances just don't capture the public imagination.