Re: How does a SAN connect to a computer?



"Ian Boyd" <ian.borlandnews010@xxxxxxxxxxxx> wrote in message news:4884eb48$1@xxxxxxxxxxxxxxxxxxxxxxxxx
i've heard of this mythical thing called a SAN (Storage Area Network). It's not a hard drive. It's not a RAID array. It's not a fileserver on the network. It's not a fast connection to a bunch of fast hard drives.

Wikipedia says that it's a special device that appears as though it's locally attached, but really it's not:

"In computing, a storage area network (SAN) is an architecture to attach remote computer storage devices (such as disk arrays, tape libraries and optical jukeboxes) to servers in such a way that, to the operating system, the devices appear as locally attached."


They indicate that a SAN is a black-box that acts like a giant hard drive, with mirroring, failover, expandable by adding more hard drives, etc.

So if it's external to the computer, you must connect to it somehow. But if it acts like a hard-drive, it must be connected line a hard-drive.

Does a SAN connect to a pc using something like external SCSI (whether it be fibre or not), or external SATA? Does it require a custom PCI expansion card to do connection?

A raid array is a big box that has a lot of disks in it. In the enterprise configurations the box appears as a set of drives that can be configured and made available to a set of mini computers or PC's (I suppose). The problem with large RAID arrays is the disks are inexpensive, but the boxes are incredibly expensive and also they provide a single point of failure. If you're data center has an outage then your company has an outage unless you have duplicate data centers, and so the costs sky rocket.

The idea with SAN, as far as I understand it, is that the box is removed from the equation. You end up with a bunch of disks in boxes anywhere in the network that you can attach to. How you attach to the drives and the protocols and so on depend on the implementation. The management software for this has to be fairly sophisticated as you can imagine. In a large enterprise it is conceivable that many raid arrays could be a part of your SAN, and likewise your SAN could consist of boxes with sata drives spread around the building/enterprise or any mix of these. It removes the single point of failure but trades it for increased management costs and network infrastructure.

hth,
Dave

.

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