Storage area networks

When it comes to the enterprise, storage is a major consideration. Attaching disks to each and every server will prove to be a massive administrative headache, not only from the point of view of physical space, but also because it will be extremely difficult to monitor and manage your storage infrastructure.

The solution to this is the storage area network (SAN). A SAN provides a central repository for all of your storage that is attached to a controller. This controller is then attached to a fiber switch that your servers then connect to.

Using the storage controller, you can create partitions (commonly called logical unit numbers or LUNs) that are presented to the server.

Figure 26-4 displays a SAN, with all of your SAN-attached servers connected to two fiber switches. These switches are in turn connected to the SAN controller, the real brains behind the storage system. It is up to the SAN controller to provide the storage from the disks connected to it, feeding this through to the servers over fiber channel (through the switches).

Note in Figure 26-4 that we have detailed a number of servers attached to two switches for redundancy. This is a very important part of a SAN; if a link to the storage goes down, then your server will not work. Redundancy of a path to the storage is something that should not be considered lightly. If you have spent the money on a SAN, then spend a little more to make it redundant.

Network Attached Storage

Another form of storage that has become increasingly popular in recent years is Network Attached Storage (NAS). Whereas a SAN is "directly attached" to the server, a NAS is accessed over the network using popular file access protocols such as Network File System (NFS) and Samba. With an NAS, the disks are directly attached to the NAS appliance and the storage is then shared out to the network. This helps to drastically reduce the cost of allocating storage to a pool of machines but decreases the reliability and the speed of accessing the data because you are sharing the networking resources to the NAS appliance.

NAS appliances usually offer features above and beyond your standard file server (which is essentially what a NAS is). One of the most popular, NetApp, provides remote mirroring to another NetApp for DR purposes and also snapshots, where you can make a copy of the data in a storage group instantly so that you can make a backup with minimal downtime to your applications. These are both technologies that until recently were available only in the storage area network space.

Switch 1

Server 2

Server 3

Switch 2

Figure 26-4: Overview of a SAN

Figure 26-4: Overview of a SAN

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