A storage area network (SAN) is a technology that allows you to attach a storage device to your network and let devices on your network, such as servers, see that storage as being locally attached. There are several options for having storage on your network, and in this article, we’ll discuss a few of them.
Direct Attached Storage (DAS) is a solution where servers have their own connection to their hard drives. This direct connection to hard drives might be internal or external. Servers are typically running a Small Computer System Interface (SCSI), which is the language that a server or computer can speak to its hard drive. When the server accesses information from the hard drive over SCSI, it’s using block-level storage, which is very efficient because it deals with bytes and bits instead of entire files.
File-level storage, on the other hand, is less efficient. It’s like having a file server on a network where you click on start, run, and type in the server name and a shared resource. This computer is seeing that server as external to itself, and it’s not seeing it as local storage. It’s using file-level access as opposed to block-level access.
Network-attached storage (NAS) is a storage device that is put on the network. It acts like a file server, and we access it like a file server. It’s using file-level storage as opposed to block-level storage. Everything is Ethernet at this point, which makes it convenient for servers and even personal computers to share a common repository of data. However, since we’re using file-level storage, the performance is not going to be there as compared to having a directly attached SCSI device.
Fibre channel is a technology that allows us to do block-level storage much more efficiently than file-level storage. In this case, we’ve got Ethernet at the top of the screen and Fibre channel at the bottom of the screen. Notice that the servers have a couple of connections going out, one for the LAN and one for the SAN. Fibre channel does give us very high-speed access to our data, but it creates additional expense and wiring requirements.
Fibre Channel over Ethernet (FCoE) is a technology that is getting popular these days in larger enterprises. We still get the benefit of Fibre channel, but we don’t have to buy an HBA for the servers, and we don’t have to have that additional cable going from the server to the Fibre channel switch. We get high-speed throughput, but it’s more expensive than another alternative out there.
iSCSI (Internet Small Computer System Interface) is another solution where the server and the storage device are connected to an Ethernet switch. Everything is running over IP, and we’re encapsulating those SCSI messages and data inside of IP packets. Because we are speaking SCSI over IP, we get to do block-level access. The technical performance is not quite as good as Fibre Channel over Ethernet, but the expense is much less than Fibre Channel over Ethernet.
In conclusion, these are a few of the storage area network options that we have available today. Depending on your needs and budget, you can choose the one that suits you best.