What is DAS, SAN, NAS

List of Topics

1) What is DAS
2) What is SAN
3) What is NAS

1) What is DAS
DAS is  known as Directly Attached Storage, which means physically a storage medium will be attached to a server eg: an USB drive, a firewire... Unfortunately this method does not have the ablity to scale.So this was not a much succesful method for storage.

2) What is SAN
SAN is known as Storage Area Network. To configure a SAN we need to attach a special device to server known as HOST BUS ADAPTER (HBA). From this host bus adapter a cable will connected to a gateway known as storage gateway. This network dedicated for storage and backup purpose is known as Storage area network. 

SAN allows multiple servers to connect to SAN network  to access centralized storage. Advantage of SAN is Maintenance and administration can be done from a  single location. 

LUN - A Logical unit which is storage attached to a server. SAN is bit expensive. and requires a special administration.

3) What is NAS
If we don't want to create a separate network for Storage we can use existing network for storage which does'nt need HBA and will communicate with NIC and existing LAN. But NAS traffic has to compete with existing LAN traffic.