Storage Area Networks
Published on Dec 17, 2015
A storage area network (SAN) is defined as a set of interconnected devices (for example, disks and tapes) and servers that are connected to a common communication and data transfer infrastructure such as Fibre Channel. The common communication and data transfer mechanism for a given deployment is commonly known as the storage fabric.
The purpose of the SAN is to allow multiple servers access to a pool of storage in which any server can potentially access any storage unit. Clearly in this environment, management plays a large role in providing security guarantees (who is authorized to access which devices) and sequencing or serialization guarantees (who can access which devices at what point in time).
SANs evolved to address the increasingly difficult job of managing storage at a time when the storage usage is growing explosively. With devices locally attached to a given server or in the server enclosure itself, performing day-to-day management tasks becomes extremely complex; backing up the data in the datacenter requires complex procedures as the data is distributed amongst the nodes and is accessible only through the server it is attached to.
As a given server outgrows its current storage pool, storage specific to that server has to be acquired and attached, even if there are other servers with plenty of storage space available. Other benefits can be gained such as multiple servers can share data (sequentially or in some cases in parallel), backing up devices can be done by transferring data directly from device to device without first transferring it to a backup server.
So why use yet another set of interconnect technologies? A storage area network is a network like any other (for example a LAN infrastructure). A SAN is used to connect many different devices and hosts to provide access to any device from anywhere. Existing storage technologies such as SCSI are tuned to the specific requirements of connecting mass storage devices to host computers. In particular, they are low latency, high bandwidth connections with extremely high data integrity semantics.
Network technology, on the other hand, is tuned more to providing application-to-application connectivity in increasingly complex and large-scale environments. Typical network infrastructures have high connectivity, can route data across many independent network segments, potentially over very large distances (consider the internet), and have many network management and troubleshooting tools.
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