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Multipathing in VMware

Posted on 2010-03-25
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Last Modified: 2013-11-14
Hi all,

I have two DL180 servers set up with VMware and the HP Lefthand P4000 VSAN. I have everything working but could use some help with multipathing. I created two iSCSI VMKernels with different NICs assigned to each. The iSCSI adapter is showing both paths to the storage. One path says Active I/O and the other says just Active. I read that to push data down both paths you have to set the iSCSI LUN Path selection to Round Robin (currently it is set to Fixed (VMware). If I set it to Round Robin on both the ESX hosts and start to do any data transfer to the VSAN iSCSI LUN, I get I/O errors because the LUN goes offline. If I leave it as is on Fixed, it works fine but doesn't seem to be using both NICs simultaneously.
Any idea why?  I must have missed something but not sure what.

thanks,
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Question by:Schnizzle
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Author Comment

by:Schnizzle
ID: 28591977
I should add that this is ESX 4.0 (VSphere), which supports multipathing supposedly.
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Expert Comment

by:jakethecatuk
ID: 28592079
I take it you've read the ISCSI guide
http://www.vmware.com/pdf/vsphere4/r40/vsp_40_iscsi_san_cfg.pdf

In particular page 20 which talks about multipathing.

How have you got your iSCSI network configured?  Are you using the same VLAN/IP Addressing scheme for both network paths?
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Expert Comment

by:jakethecatuk
ID: 28592250
Also, page 84 talks about checking the multipathing plugins and a few other things to check.
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Author Comment

by:Schnizzle
ID: 28594124
I've seen the iSCSI guide but let me take a quick review of it and get back to you, maybe i missed something there and I want to be sure I have all my ducks in a row. thanks.
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Author Comment

by:Schnizzle
ID: 28690561
Okay - I've read over the guide noted above. My multipathing setup uses two physical NICs and I have them configured just as they describe in pgs 32 - 34. As I said before, currently the iSCSI LUN Path selection for the iSCSI storage LUN is set to Fixed. This works fine - no issues but it does not load balance over the two nics, for that I have to select Round Robin and it's when I set it to Round Robin that I get I/O errors when I start pushing any decent amount of data across the NICS.
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Expert Comment

by:securitythreat
ID: 29062946
YIKES, round robin hasn't worked right yet.  It does alternate between the two paths.  However, you needs to speak with LEFTHAND to see if they are ok with that type of traffic and the SAN needs to understand it or it will cause 3 times the amount of commands for 1 command.  It will cause errors as you are sending incomplete commends to both sides.  Fixed only uses one side and will fail to the other side in case of a failure or long queue.

What is the goal you are trying to achieve and why?  Also, what type of traffic are you looking at?
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Expert Comment

by:bbnp2006
ID: 30518310
".....I created two iSCSI VMKernels with different NICs assigned to each.....", did you create both iSCSI VMKernel ports on the same vSwitch, then assign 2 pNICs to this vSwitch? or you have 2 seperate vSwitches?
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bbnp2006 earned 2000 total points
ID: 30519183
1) make sure you have multiple vmkernel port created on a single vSwitch that you want to use for the multipathing
2) for each vmkernel port group on the vswitch, you have to override the NIC Teaming configuration tab and make sure there is ONLY 1 single physical NIC is configured to be "active" for a vmkernel port, all the other pNICs MUST be moved to the "Unused Adapters".
3) Using a command-line interface to the ESX host, add each vmk adapter to the software iSCSI initiator with this command(if you are using the software iscsi initiator shipped with ESX)
4) Do a rescan to discover the multiple path.
5)Configure Round Robin path selection for all iSCSI datastores
6) in some cases, you might need to reboot your ESX host for everything to work properly.

Good luck!

Here's a detailed step by step instruction on how to configure it:

http://yourmacguy.wordpress.com/2009/11/09/vsphere-iscsi-multipathing/

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Author Closing Comment

by:Schnizzle
ID: 32853292
Works now! thanks for your help.
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Expert Comment

by:bbnp2006
ID: 32858157
good job! Glad I can help.
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