1. Directly attached disks/Storages (DAS), no RAID.
Most of home computers in home and office are this configure.
2. Directly attached disks, but with RAID
Provide better data protection. Most of small business's servers are having this configuration.
RAID 0: Striping
RAID 5: Block-level striping with distributed parity
RAID 10: 0 + 1.
3. File level shared storage
Network attached storage (NAS). used by home and small businesses. storage is provided by network. the NAS server has its own file systems and IP.
Accessed over network, usually IP network. OS sees NAS as file server.
4. Shared block level storage.
SAN is a type of shared block level storage. itself is a private network with storage linked with fiber channels and switches etc. it has no file systems, it's connected to computer via similar interface used in DAS, such as iSCSI. So usually a physical interface is installed onto computer to access the SAN.
Access over physical interface installed on computer, similar to network card. OS sees SAN as disk.
5. RAID vs SAN
storage exposed by SAN appears to hard drives to a computer, RAID can be built upon it.
SAN itself since composed by hard drives, can also be built upon RAID arrays.
One advantage of NAS and SAN is the storage is no longer attached to any specific computer so that you do not need to move storage from one server to another when a server has to be replaced. By sharing the storage among multiple applications, storage utilization is also supposed to be higher.
Below are useful illustrations from wiki.
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