iSCSI multipath vs network redundancy?

[rickardnobel]

If I am having a redundant network, say one VMkernel port on a vSwitch with two VMnic, perhaps Port ID load balancing, and the two VMnics goes to two different physical switches and there is redundant links on all switches between the ESXi host and the iSCSI SAN, and there is Rapid Spanning Tree configured, and there is some kind of Etherchannel / Link aggregation on the iSCSI server, but only one IP adress..

Is there any advantage with setting up iSCSI multipath and let the VMkernel handle the failover, instead of letting the network itself make sure there is a way between the host and the target?

[AndreTheGiant]

One vmkernel will goes only on one pNIC.

Only with IP hash and Etherchannel (on switch side) you can aggregate more links.

With multipath, and usually more vmkernel interface, you can handle more paths and use, for example, a different path for each LUN.

Andre

[mittim12]

I've always thought this blog post was an excellent read for iSCSI and vSphere.

http://virtualgeek.typepad.com/virtual_geek/2009/09/a-multivendor-post-on-using-iscsi-with-vmware-vs...

[rickardnobel]

Andrew M wrote:

One vmkernel will goes only on one pNIC.

Only with IP hash and Etherchannel (on switch side) you can aggregate more links.

With multipath, and usually more vmkernel interface, you can handle more paths and use, for example, a different path for each LUN.

Thanks for your reply! The problem with IP hash seems to be that if using only one IP address at both side all traffic will only use one of the links due to the hash based on IP SRC and IP DST.

So, the difference between network redundancy and multipath should be that you could use two paths at the same time? That is, accessing different LUNs through different IP addresses which should go by different VMnics, physical switches - to have more actual bandwidth?

[AndreTheGiant]

IP hash could be good for networking, but NOT for iSCSI network.

As I seen most storage have target that does not use link aggregation but multipath techniques.

So there is no choice... multipath as suggested by the storage vendor.

Different could be with NAS, where link aggregation is more used.

Andre

[rickardnobel]

Thanks, so if the iSCSI target does not have multiple IP addresses, will multipath do any good?

If using network techniques like Port ID/IP Hash on the Vmware side I will get only redundancy, but likely only one physical path used at the time?

And, if there is no bandwidth problem, perhaps it is not that easy to fill a 1 Gbit link if there is random access, will I have any use of Multipathing?

[AndreTheGiant · Accepted solution]

Main storage vendor use multiple IP for storage NIC (in some cases also two different networks).

With VMware multipath modules, you are limited to only one path (at a specific time) to one LUNs, but vendor could have is multipath modules, or of course you can use more LUNs to have more used paths.

Bandwith could be interesting with more VMs... or high I/O loads.

Andre

[rickardnobel]

With VMware multipath modules, you are limited to only one path (at a specific time) to one LUNs, but vendor could have is multipath modules, or of course you can use more LUNs to have more used paths.

So if I only wants failover, then multipath is not really necessary, but if having multiple LUNs that is presented behind different IP addresses on the target then iSCSI multipath could be a benefit since several VMnics (and paths) could be used at the same time?

[AndreTheGiant]

but if having multiple LUNs that is presented behind different IP addresses on the target then iSCSI multipath could be a benefit since several VMnics (and paths) could be used at the same time?

Quite correct.

Andre