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Why 2 subnets on the MD3000i ?

Posted on 2010-09-21
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Last Modified: 2013-11-14
We've been runing many MD3000i for years on one subnet for different clients.  At the beginning, we were running the MD3000i on 2 subnets on ESX 3.5  But we got into a problem when we decided to test the failover.  Dell even sent an engineer after days on testing.  They were working  with Vmware on this case.  It lasted for weeks.  

As a result they told us - as well as vmware - to use only one subnet.
 
But every article and white papers I read about the MD3000i are refering to 2 subnets.  

The big question: 1 or 2 subnets ?  And why ?

Thanks
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Question by:quadrumane
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Expert Comment

by:andyalder
ID: 33732589
Best practice is to have two independent switches dedicated to iSCSI, that dictates two subnets since if they were on the same subnet and no connection between them traffic may go via the wrong NIC port.
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by:quadrumane
ID: 33733452
Ok but is it a best practice to have 10 Gbits stacked procurve 3500 or powerconnect 6200 series one one subnet?  If the only reason to go with 2 subnets is to keep the traffic on the right NIC port Id like to know what difference it makes to have only one subnet if the switches are stacked and highy available.

Thanks again  
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by:andyalder
ID: 33733593
It's not best practice to have stacked switches as a broadcast storm can mess both of them up at the same time. You can also kill both of them at th same time by mis-configuring just one.
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Author Comment

by:quadrumane
ID: 33733819
It seems to be unlikely that broadcast storm could mess 2 stacked Procurve 3500yl-24g.  We don't use more than 4 or 5 MD3000i and 4 to 5 hosts.  

But I agree, if the switches are not configured as it should be it will kill both of them.

That told, when the switches are already stacked, well configured  and available, is there another reason to unstack it to use 2 subnets ?  
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Expert Comment

by:kevinhsieh
ID: 33739602
Just to throw in my $0.02, Dell EqualLogic requires that all controller ports be on the same subnet, though they do recommend that you connect to two different physical switches.
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Accepted Solution

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quadrumane earned 0 total points
ID: 33740452
Yes you're right about the Equalogic, 0.02 points for you ;-)  

But here is the answer for the MD3000i.   As the MD3000i is not supporting active/active path on the same controler.   In order to get 2Gbits:
NIC 0 on controller 0 on subnet 1
NIC 1 on controller 0 on subnet 2
NIC 0 on controller 1 on subnet 1
NIC 1 on controller 1 on subnet 2

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Expert Comment

by:paulsolov
ID: 33740601
Do you switches support VLANs and trunking?  How many switches do you have and how are they configured.  It may have been a network configuration limitation.

Can Equalogic trunk connection to it or does it only support failover?
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Expert Comment

by:kevinhsieh
ID: 33741217
EqualLogic supports MPIO, which is neither trunking nor just failover.
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Author Comment

by:quadrumane
ID: 33791963
I don't know about Equalogic, but yes all switches are supporting VLAN (Powerconnect 6224 and Procurve 2910al-24G in stack)

the MD3000i is also supporting MPIO and according to the Dell support engineer it does not support MCS
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