DAS (Direct-attached Storage) Direct-attached storage. This storage device is usually a disk array cabinet with multiple disks in it, but does not have a RAID function. The connection between it and the server host usually uses SCSI or FC connection. DAS can only connect to one server, and other servers cannot share the storage .
SAN
SAN (Storage Area Network) storage area network can be understood as a disk on a network. The DAS above is connected to the server through a data cable (SCSI), while the SAN is connected to the server through network equipment and network optical fibers . The structure of the SAN allows it to be connected by any server, so that no matter where the data is placed, the server can directly access the required data. This means that the same SAN can be used by multiple servers. Because of the fiber optic interface, SAN also has higher bandwidth. SAN itself does not have a file system , it is a storage device that can be connected to a network device. As long as the servers and the SAN are on the same network, the servers can connect to the SAN. From the perspective of the server's operating system, SAN is like a local disk that can be formatted and mounted.
NAS
NAS (Network Attached Storage) is a file system on the network . It is similar to the NFS service we build on one server and then share it with other servers. The NAS provider is first a server with an operating system, and then the backend of the server is connected to one or more storage devices, which can be DAS or SAN. Then the NAS needs to be on the same network as the server using it, and other servers can mount and use the file system provided by the NAS through the network
