Storage sharing

Storage sharing

Historically, data centers first created "islands" of SCSI disk arrays. Each island was dedicated to an application, and visible as a number of "virtual hard drives" (i.e. LUNs). Essentially, a SAN connects storage islands together using a high-speed network, thus allowing all applications to access all disks.

Operating systems still view a SAN as a collection of LUNs, and usually maintain their own file systems on them. These local file systems, which cannot be shared among multiple operating systems/hosts, are the most reliable and most widely used. If two independent local file systems resided on a shared LUN, they would be unaware of this fact, would have no means of cache synchronization and eventually would corrupt each other. Thus, sharing data between computers through a SAN requires advanced solutions, such as SAN file systems or clustered computing. Despite such issues, SANs help to increase storage capacity utilization, since multiple servers share the storage space on the disk arrays. The common application of a SAN is for the use of transactionally accessed data that require high-speed block-level access to the hard drives such as email servers, databases, and high usage file servers.

In contrast, NAS allows many computers to access the same file system over the network and synchronizes their accesses. Lately, the introduction of NAS heads allowed easy conversion of SAN storage to NAS.

DAS vs NAS vs SAN


Organization

[edit] SAN-NAS hybrid

Despite the differences between NAS and SAN, it is possible to create solutions that include both technologies, as shown in the diagram.
Hybrid using DAS, NAS and SAN technologies.