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Re: 10.7 - Only one FC path per LUN is registered
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Re: 10.7 - Only one FC path per LUN is registered



Hi Mandy,
	10.7 does its own FC multipathing. This has changed from 10.6 which did target based multipathing ( based on WWNN ).  On 10.7 this has changed to lun based multipathing ( based on the unique lun identifier in the device identification VPD page ).
If the target supports ALUA ( Asymmetric logical unit access ), the host will do IOs only to the target ports configured as "Active-Optimized" for a particular lun. If there is no ALUA support, all paths to a particular lun will be considered active-optimized and IOs will be done across all the paths.

Ideally if the target does not support ALUA, you should configure the luns such that a lun is visible only across the ports of one of the target controllers ( lun affinity ) to prevent lun thrashing.


-manoj


On Jul 22, 2011, at 3:23 PM, Mandy Kirkconnell wrote:

> Hello,
>
> I'm not sure if this is the right mailing list for this, but I'm desperate for answers so here goes....
>
> 10.7 only registers 1 FC path per LUN, rather than 1 path per controller as in 10.6. Does anyone know if 10.7 does its own internal FC multipathing? If 10.7 is handling multipathing in a transparent manner, is there any way to disable multipathing? Or at least a way to guarantee we are using the same physical path each I/O to prevent LUN thrashing?
>
> Ideally, we would like to be able to fine tune the FC paths down to the WWPN of the FC HBA. For example, if a dual-port FC HBA is connected to a FC switch, which is connected to both controllers of a RAID unit, we would want access to all 4 paths:
>
> FC HBA Port 1 -> FC Switch -> RAID Controller A
> FC HBA Port 1 -> FC Switch -> RAID Controller B
> FC HBA Port 2 -> FC Switch -> RAID Controller A
> FC HBA Port 2 -> FC Switch -> RAID Controller B
>
> However, at this point we would even be happy with how things were done in previous Mac OS X releases, where one path per controller (WWNN) gets registered:
>
> FC HBA -> FC Switch -> RAID Controller A
> FC HBA -> FC Switch -> RAID Controller B
>
> 10.7 11A511 (released) only registers one path per LUN, despite the fact that both controllers are connected:
>
> FC HBA -> FC Switch -> RAID Controller B
>
> This gives us absolutely no way to perform path management of our own. We are also seeing severe LUN thrashing across the 2 controllers.
>
> This seems like a major regression in 10.7.
>
> If there is a more appropriate mailing list for this topic, please let me know. I've posted these questions to the Dev Forum, with no response. I also have a bug report open with Apple, 9625043, also with no response (~45 days since opening). I really need answers to these questions. At a minimum, a better understanding of internal multipathing on 10.7, and if there are any config options to disable it.
>
> Any info, ideas or advise would be very much appreciated!!
>
> Thanks,
>
> Mandy
>
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References: 
 >10.7 - Only one FC path per LUN is registered (From: Mandy Kirkconnell <email@hidden>)



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