multiple FC link from FI to MDS switch

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May 19th, 2010
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Hi, I have multiple FC links from one FI to a MDS switch, I can only see WWPN in one of the FC ports in the MDS switch even if I have multiple FC links connected. This essentially means that only one FC link will be utilized at any one time. We workaround this by using pin group. I.e, pin Blade 1 vhba0 to use FI port fc1, pin Blade 2 vhba0 FI port fc2. Only with this, we can distribute the load across multiple FC links to the MDS. Has anyone encounter this problem before? Is it suppose to behave this way? It looks silly to me if i have 40 blades and have to do mannual pinning manually to effectively utilise multiple FC links from FI to MDS. I think i am missing some thing... Thanks Eng Wee

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Jeremy Waldrop Wed, 05/19/2010 - 03:23
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Eng Wee, the vHBAs from each blade are suppose to be automatically pinned to an FC uplink in a round-robin fashion. So if you have 4 blades and 4 northbound FC uplinks then each of the 4 blades should be pinned to one of the 4 uplinks.


If one of the uplinks fails or is unplugged the vHBAs on that uplink will get automatically re-pinned to another available uplink.


Have you tried disabling the one FC uplink to see if the vHBAs get re-pinned to the other one?


By using pin groups you lose that failover and automatic re-pinning. If the FC uplink that is linked to a pin group is unplugged or fails the vHBA in that pin group will not be re-pinned to the other FC uplink.

e-chuah Wed, 05/19/2010 - 06:12
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Hi Jeremy,  >the vHBAs from each blade are suppose to be automatically pinned to an FC uplink in a round-robin fashion. So if you have 4 blades and 4 northbound >FC uplinks then each of the 4 blades should be pinned to one of the 4 uplinks. In my scenario, it doesn't look like the case. I only see all WWPN in one of the FC links. To achieve what you describe, i believe there is no need to do any configuration on UCS manager.  >Have you tried disabling the one FC uplink to see if the vHBAs get re-pinned to the other one? Yes, if i disconnect one FC link, i can see the WWPN in the other FC link. This works fine.  I am running 1.2.1(b)   Thanks Eng Wee

shamilton-wilkes Wed, 05/19/2010 - 10:59
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Yes that's exactly as it's supposed to work right now.  Trunking is coming is a later release I beleive.

gdragatsis Tue, 05/25/2010 - 05:18
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Intersting observation.


I too have had a similar experience (not on the MDS's though) but on a pair of Brocade SIlkWorm200E's. Indeed I had configured two FC uplinks from each FI to each Broc. Both ports on FI_A uplinks where configured as the same VSAN (Internal UCS usage) and the the same for the other FI (different VSAN offcourse).


WIthout any adminitsrative pining (manual), each vHBA (2 from 3 B250's with M71KR-Q's) did a flogi on port 5. The third blade did a flogi thorugh port 6 tp the brocade. So after zoning (using pwwn) and the rest, I disabled port 6 and found that the blade lost connectivity from the storage array. I was expecting it to dynamically pin to port 5.


I then had to re-enable the disabled port and what do you know, I was able to scan and represent my storage.


So the questions I have are:


  • Why did this not work?
  • If we are able provide multiple FC uplinks for load balancing and seeing as htis does not work we cannot really design for any throughput requirements that may require more that one FC uplink. Apart from manual  pinning (which defeats the purpose of load balancing) load balancing does not work. Is this a correct statement based on my experience?


gd

Randall White Tue, 06/22/2010 - 13:27
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I recently added 3 more FC ports from a 6120 to an MDS-9124 FC switch.

I am not using SAN pinning.

I found that the vHBAs were only showing up in the FLOGI table on the original FC port.

Once I rebooted all of the blades, then I saw an even distribution across all 4 FC ports in the FLOGI table.

I guess this makes sense, I keep forgetting that FC doesn't act like Ethernet


Randy

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