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  • 1.  Can I use VDS with LACP to reduce iSCSI connections on SAN group?

    Posted May 22, 2014 05:11 PM

    I'm trying to reduce the number of iSCSI connections to my EqualLogic storage group. I am currently using a standard vSwitch with two vmk ports per server for SAN. Can I use a single vmk with VDS/LACP to reduce my iSCSI connections by half per server and still maintain bandwidth/redundancy?

    I'm fairly confident this will work, but was hoping for validation. Please correct me if I'm totally off or if this would be unsupported.



  • 2.  RE: Can I use VDS with LACP to reduce iSCSI connections on SAN group?

    Posted May 22, 2014 09:48 PM

    I think what you're asking is if using LACP will utilize multiple network adapters with a single VMkernel port. And the answer there is: no.

    Will traffic flow to your storage array? Yes.

    The ESXi host will inspect its routing table, search for a VMkernel port on the same subnet as the iSCSI target (or otherwise use the default gateway), and then throw the session over to LACP to hash out an uplink choice. This uplink choice will not change unless there is a link failure. At that point, traffic will be shifted to the surviving link.

    I go over iSCSI in great detail in the Networking for VMware Administrators book.



  • 3.  RE: Can I use VDS with LACP to reduce iSCSI connections on SAN group?

    Posted May 23, 2014 01:42 PM

    In my case I am using 10GbE so I'm not sure I would need more than a single active port per host (I'm still working to scale this out).


    My volumes span multiple physical devices (20 paths for 7 volumes per iSCSI adapter). Can I assume that with load balancing on a LAG set to hash both source and destination, I would get at least some load balancing between adapters?


    If I do choose a LAG, I'm having trouble visualizing how it might reduce my iSCSI connections to my storage pool. I'm configuring the targets on my Broadcom adapters, the vmk connects through those adapters. Is the logic smart enough to only connect active paths on one adapter or another in a LAG? I'm not even sure I'm making sense anymore :smileywink: I might have to play with a LAG on an isolated host for a bit and see how exactly it will behave.



  • 4.  RE: Can I use VDS with LACP to reduce iSCSI connections on SAN group?
    Best Answer

    Posted May 23, 2014 02:32 PM

    My volumes span multiple physical devices (20 paths for 7 volumes per iSCSI adapter). Can I assume that with load balancing on a LAG set to hash both source and destination, I would get at least some load balancing between adapters?

    If you have multiple L2-4 target endpoints, yes. Such as an IP address, MAC address, or unique ports. Paths, volumes, and devices are not relevant to LACP.

    If I do choose a LAG, I'm having trouble visualizing how it might reduce my iSCSI connections to my storage pool. I'm configuring the targets on my Broadcom adapters, the vmk connects through those adapters. Is the logic smart enough to only connect active paths on one adapter or another in a LAG? I'm not even sure I'm making sense anymore :smileywink: I might have to play with a LAG on an isolated host for a bit and see how exactly it will behave.

    The adapters are no longer exposed. The LAG forms one logical interface. Traffic can be sent or received across any physical adapter in the LAG.

    Note: I would not use a LAG for iSCSI traffic on a vSphere host: Seriously, Stop Using Port Channels for vSphere Storage Traffic | Wahl Network



  • 5.  RE: Can I use VDS with LACP to reduce iSCSI connections on SAN group?

    Posted May 23, 2014 04:21 PM

    Thanks, I was starting to have doubts about configuring a LAG for the iSCSI traffic earlier today when I had a chance to think about it in more detail. I can find other ways to optimize the iSCSI connection count.

    Thanks for the help!



  • 6.  RE: Can I use VDS with LACP to reduce iSCSI connections on SAN group?

    Posted May 23, 2014 01:30 AM

    This would maintain redundancy assuming the upstream physical switch supports multi chassis etherchannel (like Cisco VPC), but it wouldn't maintain the bandwidth of two iSCSI connections. LACP is only going to hash the connection to a single link, to take advantage of the multiple links in an LACP etherchannel you are going to need multiple IP addresses.

    I haven't tried ISCSI on LACP, I know there are some checks when you bind the ISCSI vmkernel to the virtual storage adapter. I believe one of the checks is that the VMK is only active on a single link, but I'm not sure. It's been a little while since I set up ISCSI.



  • 7.  RE: Can I use VDS with LACP to reduce iSCSI connections on SAN group?

    Posted May 23, 2014 01:47 AM

    I haven't tried ISCSI on LACP, I know there are some checks when you bind the ISCSI vmkernel to the virtual storage adapter. I believe one of the checks is that the VMK is only active on a single link, but I'm not sure. It's been a little while since I set up ISCSI.

    The checks verify that only a single network adapter is marked Active and that all other adapters are marked Unused. Keep in mind, however, that Enhanced LACP with a 5.5 VDS creates a single uplink object to represent the LAG - it no longer uses the individual network adapters in the teaming policy.

    It also verifies that the storage array is layer 2 adjacent by checking the hops to the target (routed iSCSI binding is not supported).