SANs make effective use of Fibre Channel networks and IP networks to solve the distance and connectivity problems associated with traditional DAS solutions such as parallel SCSI. In a SAN, a device can be added or removed without any impact on I/O traffic between hosts that do not participate in the configuration change. A host can reboot or disconnect from the SAN without affecting storage accessibility from other hosts. New arrays can be added to the SAN,and storage from them can be deployed selectively on some hosts only without any impact on other hosts. Thus, SANs enable dynamic, non-disruptive provisioning of storage resources.
SAN architecture allows for multiple servers to easily share access to a single storage array port. This is technically possible with parallel SCSI too, via the use of daisy-chained cables. However, the setup is static, physically cumbersome, subject to practical constraints from requirements on signaling integrity, and difficult to establish and maintain.
SAN architecture also allows for a single host to easily connect to a storage frame via multiple physical and logical paths. In a multipathed configuration, and with the use of multipathing software such as Powerpath, the host experiences I/O failures only if every one of its logical paths to the storage array fails. Multipathing software can also help balance the host’s I/O load over all available paths. Multipathing capability thus allows for the design of a high performance, highly available, redundant host system.
SANs make it simple to consolidate multiple storage resources – such as disk arrays and tape libraries - within a single physical or logical infrastructure. These resources can be selectively shared across host computers. This approach can greatly simplify storage management, when compared to DAS solutions.
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