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King Chung Huang · Feb 10, 2003, 03:39 PM

In the following diagram from Apple's Xserve RAID Deployment page:

How do the four Xserves decide which drives each one can access? Can all four servers read/write from the same volumes at the same time? Or, do they "capture" a volume for themselves?

I've also read about SAN management software for Fibre Channel. Is it required in this situation? Or will plugging everything in allow shared access to the Xserve RAID's volumes?

laxthxdude · Feb 10, 2003, 03:55 PM

Think of the fiber switch as a "hub/switch" as in an ethernet environment. The XRaid is configured via the management module to carve the storage into sections. For example, 4 of the drive maybe used on one of the servers for FTP. This storage is setup on the XRaid via management console. Once this is done, the configuration is much like connecting to a normal shared storage disk over a network. All of this is done via the management configuration console.

The Mick · Feb 10, 2003, 07:45 PM

The above explaination is good. Typical SAN environments like the one in the diagram require some type of SAN management software to allow simultaneous access by multiple servers to the different areas of the SAN array. Since Apple has this diagram listed, I would assume their software allows for this arrangement.

King Chung Huang · Feb 11, 2003, 12:26 AM

Thanks for the info! By management software, do you mean stuff like Rorke's ImageSAN? I've been looking at FC management software, and I'm being quoted costs ~US$4500 for three stations! What would happen if there wasn't any management software? Would it become a free-for-all, or would none of the servers be able to see the volumes in the Xserve RAID?

I did notice that Apple says, "Also included in RAID Admin are advanced Fibre Channel networking features such as LUN masking, which enables you to make storage volumes accessible to specific host systems while masking them from others on the Fibre Channel network." Is this sufficient to control Fibre access to the Xserve by multiple Xserves? Would the Xserves be able to share the same volume for reading data?

Thanks in advance for any info you can give me!

geekwagon · Feb 11, 2003, 03:11 PM

I did notice that Apple says, "Also included in RAID Admin are advanced Fibre Channel networking features such as LUN masking, which enables you to make storage volumes accessible to specific host systems while masking them from others on the Fibre Channel network." Is this sufficient to control Fibre access to the Xserve by multiple Xserves? Would the Xserves be able to share the same volume for reading data?

Thanks in advance for any info you can give me!

LUN masking would do the task, you just need to be sure to set it up correctly on each host connected to the SAN, which is obviously a manual process.

In the Unix world, we usually also run some kind of volume mangement software such as Veritas that will also prevent the hosts from touching disks that are currently mounted to other hosts. Not foolproof but another layer of safety.

As for sharing the same data on multiple hosts, the answer is NO, at least not without somekind of global lock manager. I have never seen one for OS X although they do exist for Solaris and NT. Dunno if Oracle is supported on OS X but if you bought the right options you can have multiple machines use Oracle RAW volumes as well (Oracle has its own built in lock manager)

tiborg · Feb 12, 2003, 02:45 AM

The Xraid specs mention supporting a fibre channel loop, so would that mean I could take 3 XRaids and a an XServe and simply daisy chain them together with the last XRaid on the loop connecting back to the XServe?

geekwagon · Feb 12, 2003, 05:24 AM

Originally posted by tiborg:
The Xraid specs mention supporting a fibre channel loop, so would that mean I could take 3 XRaids and a an XServe and simply daisy chain them together with the last XRaid on the loop connecting back to the XServe?

Hmm. I don't think so. Everything I have worked on has had hubs and they always call it a "loop." I think it is a loop in the same sense as token ring is a "ring" it is just a virtual loop inside the hub.

I could certainly be wrong though. Never tried it!

tiborg · Feb 12, 2003, 06:41 AM

Yeah, I read the documents more closely and saw that Apple mentions you need a hub for the loop.