Upgrading a Xserve RAID plant

[shamrockdoc]

Hi,

We currently have a Xserve G5 with two PCI Fibre Channel cards, each directly attached to a 3.5GB Xserve RAID. Each of these 3.5GB RAIDs is fully populated and its two volumes are striped by the server.

We are adding a new 7TB Xserve RAID to this setup; hence we need to convert to FC switching. We are not running Xsan and do not wish to start (we can’t run the fiber to our client workstations), so this is really best viewed as a high-performance NAS rack.

Apple’s generic Xserve RAID documentation implies that we can only run one FC cable from host to the FC switch. But the Xsan documentation pretty clearly states that multipathing is supported. And a search of the forums here yields an article https://www.afp548.com/forum/viewtopic.php?forum=18&showtopic=13659 implying that multipathing is actually in Mac OS X Server. However, there don’t seem to be any multipath configuration tools in Mac OS X server (The Xsan bundle has a utility that allows one to set the multipathing mode).

1. If I attach multiple FC cables from the host to the switch, will multipathing “just work”, assuming I have the FC switch ports configured correctly? I suspect that it won’t, that the server will see each volume twice. But I can’t find what setting should be twiddled to make this work. The “fibreconfig” program seems to be the back-end for the Apple Fibre Channel Utility and didn’t seem to add new functionality.

2. Is there any point to going above two paths from host to switch? As I noted, I have two FC adapters so I could go up to 4… I could do one from each adapter as well, instead of two from the same adapter.

3. Any other “gotchas” when migrating from direct-attached Xserve RAIDs to switched operation? I assume the server will sort out the arrays based on the WWNN information (each of the Xserve RAID’s two volumes are striped by the server).

4. Are we idiots for NOT going the Xsan route in this situation? I would expect our storage needs to continue to increase, but the majority of our clients are stuck with Ethernet and there’s little hope of a change any time soon.

Thanks!

Doc

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