1) Share storage among different application servers.
2) Data is stored at a block level.
3) Physical elements of the SAN (servers, switches, storage arrays, etc.) are connected with Fibre Channel.
4) SAN is both scalability and flexibility.
5) Storage can be added without disrupting the applications and the different types of storage can be added to the pool.
5) Backups are centralized due to reducing workload and also providing greater assurance that the backups are complete.
6) Backup traffic never impacts users on the LAN.
ISCSI SAN Advantages
1) iSCSI is a lower cost alternative to Fibre Channel SAN infrastructure.
2) Interconnect is ethernet cable and the switches are Gigabit ethernet.
3) Protocol used is TCP/IP.
iSCSI presents volumes as a block storage device which makes them ideal for use by enterprise applications such as Microsoft Exchange and Microsoft SQL Server. In particular, the Microsoft iSCSI Software Initiator is the component of the overall iSCSI environment that makes it possible to make the iSCSI SAN attached disks appear to be local attached disks.
DAS (Direct Attached Storage) Advantages
1) The disks may be internal to the server or in an array that is connected directly to the server.
2) Backups must either be performed on each individual server.
3) Storage can only be added by taking down the application server, by adding physical disks and then rebuilding the storage array.
NAS (Network Attached Storage) Advantages
1) NAS accesses data by file.
2) NAS manages its own file system.
3) NAS can be accessed across multiple operating systems.
4) NAS backups are more efficient. (With NAS feature called Snapshot provides an almost instantaneous way for the systems administrator to recover lost, deleted or corrupted files.)
5) Administrators can assign shares and security settings as they would for a regular file server.