Single controller, dual controller
Entry level storage systems come with single controller. If one controller fails there is no alternate path for the data. Dual controller systems give full redundancy. With good management software dual controller systems give load balancing and path failover features and ensure high availability. iSCSI, Fiber channel interface iSCSI interfaces offers lowest cost with 1 GBp/s interface with host systems. With host systems there is distance limitation 20 m.Fiber channel interface gives maximum data transfer of 4GB/s swith the host systems. With fiber channel interface you can also eliminate the distance barrier with the host servers.
Your systems should be scalable to your growing requirements. You can choose different models which can host 12 HDD, 24, 40, 60, 90, 200 etc. The number of host servers that can be connected to the system is another criterion of expandability.
Backup and restore
For backup and restore tapes are being used as offline storage. As said earlier since these systems are slow you need to compromise on the recovery time. Now the hard disks are getting cheaper and the business is moving to have online systems with NAS and SAN. Files servers, data base servers, application servers and operating system images are being backed up. You need appropriate software and connectors/plug-in/API for backing up different applications and different database systems. Modern IT infrastructure heavily relies on virtualization. You need appropriate management systems to back up and restore virtual machines.