主题：NAS or SAN? -- ppw

如果不是大机构,不需要用上几个Rack的Database的话,根本就不用考虑SAN.

A SAN is a dedicated storage area network that is interconnected through a Fibre Channel protocol using either 1-gigabit or 2-gigabit Fibre Channel switches and Fibre Channel host bus adaptors. Devices such as file servers connect directly to the storage area network through the Fibre Channel protocol. Unlike a NAS filer, which uses standard TCP/IP over Ethernet to connect the storage to the network, SANs use Fibre Channel protocol to connect storage directly to devices/hosts.

NAS connects directly to the network using TCP/IP over Ethernet CAT 5 cabling. In most cases, no changes to the existing network infrastructure need to be made in order to install a NAS solution. The network-attached storage device is attached to the local area network (typically, an Ethernet network) and assigned an IP address just like any other network device.

SANs are highly redundant through the implementation of multipathing and the ability to create fully redundant fiber meshes; so there is no single point of failure. SANs feature block-level transfers instead of NAS file-level transfers. This is critical if you have database applications that read and write data at the block level.

SAN products run on Fibre Channel protocol and are entirely isolated from the IP network, so there is no contention over the TCP/IP offload engine (which optimizes throughput). NAS products run over your existing TCP/IP network, and, as such, are prone to latency and broadcast storms, and compete for bandwidth with users and other network devices.

With a SAN, there is higher security because SAN uses zoning and logical unit number (LUN) security. NAS security is typically implemented at the file-system level through traditional operating system access-control lists.

There is more flexibility for redundant array of independent disks (RAID) levels. While NAS products do support standard RAID levels, such as 0,1,5, you typically do not get the flexibility to mix RAID levels within the same device.

[SIZE=3]LOWER COSTS WITH NAS[/SIZE]

File servers see SAN attached volumes as locally attached disks, whereas a NAS presents them as remote network file system (NFS) or new technology file system (NTFS) file shares. NTFS is the file system that the operating system uses for storing and retrieving files on a hard disk.

NFS is a client/server application that lets a computer user view and optionally store and update files on a remote computer as though they were on the user’s own computer. Some applications do not support remote drives and can only use a volume that is local to the OS.