Call me slow, but I’ve only recently come to understand what the Xserve RAID really is, and it’s not just a RAID.
Before my revelation, I had figured that, out of the box, the Xserve RAID was strictly a DAS RAID device, connecting via Fibre Channel to a single Xserve, much like the SCSI RAID boxes we already have connected to servers of several stripes in our server room. Yes, the Xserve RAID can work this way, but as I found, it’s not the only way. I also confess that though I was aware of Apple’s Xsan software, I thought that only with it could you turn the Xserve RAID into a true multi-hosted SAN.
It’s not that Apple doesn’t clarify this on their site, but I never looked into the details until it was time for us to purchase a SAN solution. Now that I have looked, I would suggest calling the Xserve RAID the “Xserve SAN” or even the “Apple SAN”, since out of the box that’s what it is, whether you run it with Xsan or not.
So, not only will the Xserve RAID work as a DAS, but you can also plug one into a Fibre Channel switch, and its volumes will be available as local storage to the servers on that switch (none of which have to be Xserves), making it a true SAN device.
What Xsan adds to this, then, is the means for multiple servers to access the same Xserve RAID volumes concurrently. This is something valuable in more collaborative environments like video production, but it’s nothing we would need for hosting our mail, file, or data stores that are accessed only by their respective servers.
This turned out to be a big deal since even when I considered an Xsan system, which requires two Xserve boxes to run, its price was still about half that of other FC or iSCSI solutions I was looking at. Not bad, but now that I know I can have an Apple SAN without Xsan, I’m looking at a price of roughly one quarter of that for the other candidates, and that’s very hard to pass up. Granted, I’d be missing out on some features that come with the higher-end solutions, like redundant controllers or volume snapshotting, but this would be acceptable for our purposes (those looking for a complete failover solution might be interested in the Vmirror).
The final point to consider now is whether the Xserve RAID can perform with the reliability of the boxes costing four times more. Even I, an Apple defender to the end, have had my doubts, but when one enterprise software vendor gave me an unsolicited recommendation for Apple storage, I began to consider the Xserve RAID seriously. Most reports I’ve found on the web generally agree that the Xserve RAID, especially for the price, is a solid solution, so I’m becoming convinced. We might very well see a couple “Xserve SANs” in our server room very soon.