Using Xserve RAID as NAS

Use some caution on the terminology here, as there are Xserve and Xserve RAID widgets, and these are quite different.

There needs to be a computer or controller here to act as a router between clients expecting to have Network Attached Storage (NAS) and a Fibre Channel Storage Area Network (FC SAN) widget such as the Xserve RAID.

There are controllers which allow SAN storage to be served via network, but these typically operate by providing a complete separate path (NAS) into the storage. Via iSCSI or AFP or SMB into the controller, for instance. (And I'd expect there isn't much in this product space for an Xserve RAID array; I am aware of a few vendors that do offer storage arrays that can be acquired with one or both of iSCSI and SAN bus interfaces, but Apple doesn't AFAIK offer this with Xserve RAID.)

I'd probably look to sell the Xserve RAID and (if you have it) the FC SAN Host Bus Adapter (HBA) you were using, and use any profits to offset the cost of acquiring a replacement NAS storage array widget, or to acquire a Direct Attached Storage (DAS) storage array that can be served off one of your existing host(s). A SCSI or SAS shelf hanging off FireWire 800 or a SAS controller can do quite well in this regard.

I'd tend to guess you'll spend more - if you don't already have a Mac Pro or Xserve and FC SAN giblets you can connect to the Xserve RAID - than wholesale replacement with a DAS or NAS widget. 5.6 TB is approximately three current-generation disks, or four of the previous 1.6 GB generation disks. A four- or eight-bay Drobo is in this range, as are many other solutions. Or "just a SCSI or SAS storage shelf" configured as DAS can work fine, too. (And disk storage shelves are available from various vendors.)

Simple answer: no.

Not without spending more than you probably would with purchasing something (else) specifically intended for use as a NAS widget.

Fibre Channel (which is what the connection into the Xserve RAID is called) and Ethernet are entirely different technologies.

The gear you will need to adapt from Ethernet to Fibre Channel and into your Xserve RAID will be expensive and complex. You'd here need something akin to that Xserve computer, and Mac OS X Server software, to get from the Ethernet to the Fibre Channel, and to the Xserve RAID storage.

Sell the Xserve RAID storage box to somebody else that is already using Fibre Channel storage, and buy or build a purpose-built NAS widget.

A TimeCapsule with (if you need more storage than the base disk) external USB storage connected can do fairly well here as a NAS storage device, depending on how much performance you require. And it supports Time Machine backups.

And I specifically intend widget and giblet to mean "parts" or "pieces" or "boxes." Unspecified building blocks.

Maybe you're saying that the fibre channel port on the RAID needs to be connected only to a fibre-channel card on a single CPU at the same time

That's exactly how it works.

My thought was to convert the fibre channel port on the Xserve to ethernet

Assuming you mean "... on the XServe RAID", no, that cannot be done. The XServe RAID only transfers disk-based data over fiber channel. That can be connected to any host computer, and that computer can then re-share that volume to other network clients, thereby achieving a NAS-type infrastructure, but you will need a connected server continuously running to make the drives available to network clients.

There is one variation to this, which is a SAN - in this way everyone connects to the RAID via fiber channel, but it involves fiber channel cards on every machine, a fiber channel switch, and some dedicated hardware to take care of arbitration (to make sure two people don't write the same file at the same time). It's a somewhat costly option.

I was only seeing if one could make the fibre channel ports on the Xserve work over gigabit ethernet.

In short, not directly, only through some other server that's talking gigabit ethernet.