SAN multipathing in OS X 10.5 Leopard

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SAN multipathing in OS X 10.5 Leopard

Hello,

Would anyone be so kind as to clarify for me the multipathing support for FC SAN connections in OS X Leopard both server and workstation? Is there support natively or do I need to purchase an extra tool like Xsan?

I would like to connect a number of MacPros to a FC SAN and would like them all to be multipathed. Each MacPro has 10.5.6 and an Apple dual port FC HBA fitted. They are connected to a NetApp FAS3040 SAN via a set of Brocade switches. If I connect them up multipathed "as-is", each LUN appears in the Disk Utility multiple times just as if there was no multipathing software configured. What do I need in order to set up the multipaths so that each LUN only appears once?

Many thanks,

Richard.

MacBook 4.1, Mac OS X (10.5.6)

Posted on Mar 4, 2009 4:42 AM

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Answer 1

Mar 4, 2009 8:14 PM in response to Richard21

Multipathing should "just work" as of 10.5.2.

That said, the last time I tried connecting an Xserve to a NetApp over fibre there were issues -- mainly because the NetApp performance was not good (this was 6 shelves of 14 fiber drives). The NetApp insisted on doing "housekeeping" every 45 seconds or so and as such could not support uncompressed SD without dropping frames.

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Answer 2

Richard21 Author

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Mar 10, 2009 5:00 AM in response to William Lloyd

You are quite right, it does "just work", but it appears to work in a different way from most other implementations.

I have found through experimentation that when multiple paths are presented to the same disk array controller port, then OS X does indeed multipath the LUNs. But when multiple paths are presented that go through different controller ports, then the LUN appears once for each controller port. So if you have connected in 2 controller ports, the LUN appears twice, 3 controller ports, you get 3 LUNS etc. Therefore, it looks like OS X virtualises the target and not the LUN.

This is very irritating, to multipath correctly in OS X, this means that the disk array you buy has to support controller virtualisation. The NetApp ones do through the "Single Image" mode where all controllers appear as 1 device (a single WWN). It would be good if OS X virtualised the LUN like most other multipathing solutions.

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Answer 3

urendels

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Mar 10, 2009 5:46 AM in response to Richard21

Hello Richard,
your are right with your conclusion. Leopard is not using a LUN-Multipathing and therefore the same LUN appears twice if the second storage-controller has his own WWNN. You would need to run with the same WWNN or with a different HBA/driver.

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Answer 4

Mar 24, 2009 6:17 PM in response to urendels

Proper multi pathing is NOT possible with automatic fail over with the Promise Raids and OSX.

According to the Promise Web site

“ Please have in mind the following: we present unique WWNN (World Wide Node Name) per controller. We do LUN based as apposed to Target based implementation;”

http://kb.promise.com/article.aspx?id=10081&query=multipathing

From the Apple Dev web site

http://developer.apple.com/technotes/tn2007/tn2173.html

Mac OS X provides multipathing support on a per-target basis. Multipathing at the LUN level is not currently supported.

This dates back to 10.3.5 and has not changes since.

BRETT

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Answer 5

May 26, 2009 8:56 AM in response to Richard21

How did you make the luns appears in Disk Utility ?
I'm running a problem that I can't "see" any target

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Answer 6

May 27, 2009 2:03 PM in response to Ofer Arbeli

They should just appear. You don't have any zones set on a switch? Try rebooting the host.

Note: This is really a threadjack, as your question has little to no relation to the post at hand.

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