Enable or disable Spanning Tree in iSCSI switches

Posted on 2011-10-18
Last Modified: 2012-05-12
I am trying to determine to some reasonable end the best practice regarding STP being enabled or disabled on an iSCSI network.

The configuration is such that there are 4 stacked switches all dedicated to the iSCSI fabric. That is, all that connects to the stack is the storage array iSCSI interfaces and the hypervisor iSCSI interfaces. Although there is one additional connection just for management of the stack. There is MPIO/Multipath enabled on the endpoints.   The stacking is accomplished with stacking cables, i.e. not ethernet uplinks between switches.

Hopefully that is sufficient information.

In performing the preliminary research, most documentation regarding configuring a switch for iSCSI states that STP should be disabled on ports that handle iSCSI end-points.  Often in the documentation there is a caveat that states if you do want to run STP then the portfast option should be enabled on those ports as well.  -- assuming Cisco here.  There is often no  further explanation as to why STP would be present, so I am assuming the documentation assumes that in some cases the switch/stack may not be dedicated to iSCSI and may be connected to another non-iSCSI network, or there may be cases where the potential for connecting into another switch, or between switches may be possible.

Personally I do not see the need for STP in a iSCSI dedicated stack of switches, and I would be inclined to disable it switch/stack wide.  I see STP as just a safety precaution and eventually just an unnecessary configuration burden if it were implemented for that sole purpose in a highly controlled environment.

Is my position incorrect, and if so why?  

Welcome to all options and facts.

Thank you.

Question by:BladesAway
    LVL 33

    Expert Comment

    I'm not aware of any good reason to run STP on a dedicated iSCSI stack.

    Author Comment

    Is there any negative to running it?   I'm thinking that one negative is that it becomes an unnecessary configuration item if it is not needed for a specific purpose -- thus it could potentially cause issues if it is not turned off on a port handling a iSCSI end-point.
    LVL 33

    Accepted Solution

    I wouldn't necessarily expect it to cause any problems.  There might be some overhead, both in administration (as you point out) and processing.  As a rule, if it's not necessary, why turn it on?

    Author Comment

    Agreed.  Your point is exactly the point I am trying to make to those I am trying to explain this too.   The goal is to keep things lean.

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