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SAN Buying Guide
Storage Area Network (SAN) units are expandable so you can have multiple trays and get a very high capacity of storage. The drives are controlled by controllers in the SAN and these handle all the raid configurations. The SANs usually have dual controllers and dual PSUs for redundancy.
You can get SANs with 2.5" and 3.5" drives but you can't mix and match shelves. SANs are available in 1Gbe, 10Gbe and Fibre connectivity. Fibre is the fastest but also the most expensive as fibre switches are very expensive. SANs are needed to run virtualisation as the data and vms need to be stored on the san so multiple servers can access them. Pros: good read/write speed, high data capacity, multiple servers can access the data, good redundancy.
SAN moves storage resources off the common user network and reorganizes them into an independent, high-performance network. This allows each server to access shared storage as if it were a drive directly attached to the server. When a host wants to access a storage device on the SAN, it sends out a block-based access request for the storage device.
A storage-area network is typically assembled using three principle components: cabling, host bus adapters (HBAs) and switches. Each switch and storage system on the SAN must be interconnected and the physical interconnections must support bandwidth levels that can adequately handle peak data activities.
Storage-area networks are managed centrally, and Fibre Channel (FC) SANs have the reputation of being expensive, complex and difficult to manage. The emergence of iSCSI has reduced these challenges by encapsulating SCSI commands into IP packets for transmission over an Ethernet connection, rather than an FC connection. Instead of learning, building and managing two networks -- an Ethernet local-area network (LAN) for user communication and an FC SAN for storage -- an organization can now use its existing knowledge and infrastructure for both LANs and SANs.
A virtual storage-area network (VSAN) is a software-defined storage offering that is implemented on top of a hypervisor such as VMware ESXi or Microsoft Hyper-V. Virtual SANs yield a number of benefits such as ease of management and scalability. For the most part, VSANs are hardware-agnostic. As long as the storage hardware is recognized and supported by the hypervisor, the hardware can be used by the VSAN (although each vendor has its own requirements).
Unified SAN is based around the concept of unified storage, which exposes file storage and block storage through a single device (usually a modified NAS appliance).