13 Replies Latest reply: Nov 18, 2013 11:59 PM by hameed264@gmail.com RSS

SNMP vs WMI polling - pros and cons

Leon Adato

I'm pulling together a (semi-comprehensive) comparison of the impact of monitoring via WMI versus SNMP.

 

The upshot for those who are impatient: WMI monitoring (whether WMI polling or WMI via SAM) has a measurable - but manageable - impact on both the target device and the poller.

 

That said, if you are considering converting your monitoring of Windows devices from SNMP to WMI, what are you gaining? What are you losing?

 

Here's the start of my list. Please add your own in the comments below. Note that this is an off-the-top-of-my-head list. Coherency comes later.

 

SNMP Monitoring (as compared to WMI)

  • CON Cannot monitor Windows Volume Mount points
  • CON Challenges configuring earlier versions of Windows (NT, W2k)
  • CON Requires additional non-default configuration actions (enabling snmp agent, setting RO string, etc)
  • PRO Fewer ports for enterprise firewall rules (translates to an easier time getting security to agree to variances)
  • PRO No single point of failure for access
  • CON Changing SNMP string requires enterprise-wide changes
  • CON Uses SNMP service start time for uptime metrics, rather than actual server reboot time
    • Work-around: set up UnDP for hrSystemUptime
  • PRO Extremely efficient use of CPU, RAM and bandwidth (on both target and poller)

 

WMI Monitoring (as compared to SNMP)

  • CON WMI-only devices cannot use custom pollers (UnDP).
    • Work-around: If the machine has EVER been an SNMP polled device, the snmp info is retained and custom pollers can be used (at least until the SNMP RO string changes)
  • PRO Account settings used by SAM automatically
  • CON significantly more firewall ports required
    • Work around: per-server config can nail down WMI to just a couple of ports
  • CON will not work across a NAT-ed WAN connection (VPN, etc)
  • CON one password change in AD can cripple monitoring
  • CON cannot monitor topology
  • PRO doesn't try to monitor RAM as a volume (why does NPM do that, anyway?!?)
  • PRO uses REAL reboot time for uptime metrics
  • CON less efficient (vis a vis SNMP) use of CPU, RAM and bandwidth on both target and poller

 

OK guys, there's the start of my list. What did I miss?

  • Re: SNMP vs WMI polling - pros and cons
    bsciencefiction.tv

    This is very timely for us.  We are actually putting together this discussion now with Server 2012 stating it will have degraded SNMP and I can only assume after 2012 it will only get worse.

     

    We are really having to dot our i's and cross our t's, because as I have stated in previous posts, our Data Security is run like the TSA and their concept of security is if you tell everyone "no" you have secured the environment.

  • Re: SNMP vs WMI polling - pros and cons
    byrona

    WMI is much slower than SNMP.  With Server 2012 WMI is even slower than it used to be.  I generally always use SNMP when possible and use WMI as my 2nd option when necessary because of the speed.  Also, WMI tends to be more "buggy", I have never really had problems with SNMP as it's much more reliable.

     

    Nice list though, I look to what others have to say!

    • Re: SNMP vs WMI polling - pros and cons
      mdriskell

      I concur with byrona I prefer SNMP.  Now that being said I will make some nodes WMI based when I upgrade to 5.5 because of the ability to poll mount points.  It's really a shame however that there can't be a blended approach.  I mean it's completely possible to build a SAM poller for a WMI query on an SNMP node but if the node is WMI based it's not possible to do any SNMP monitoring unless like the other user said it used to be SNMP at one point.

      • Re: SNMP vs WMI polling - pros and cons
        familyofcrowes

        Totally agree....  SNMP is faster and when you have 15,000 elements its much nicer to the CPU and polling intervals.

         

        We use WMI for our almost 700 applications and if there are alot of components it can sometimes timeout.

         

        I say use SNMP for basic monitoring and WMI for the detailed items like applications....


  • Re: SNMP vs WMI polling - pros and cons
    mdriskell

    This is something I ran into a while back in regards to WMI having an issue.  WMI utilizes reverse lookup for confirmation so an invalid reverse lookup can cause WMI to fail.

     

    http://thwack.solarwinds.com/message/161528#161528

  • Re: SNMP vs WMI polling - pros and cons
    bspencer63

    I prefer SNMP and also wouldn't like to lose all of my historical data by converting a node from SNMP to WMI or vice versa.  Since most all of my nodes were setup via SNMP I will stay the course barring any tremendous WMI improvement gains that would peak my interest again.

  • Re: SNMP vs WMI polling - pros and cons
    footerest

    As a DoD admin SNMPv2 is now prohibited from being used.  We are being forced to use WMI to poll all our Windows servers.  Interface statistics are available via WMI directly.  Why can't NPM pull interface statistics using WMI?  Any hope for the capability to be added in the future?

    • Re: SNMP vs WMI polling - pros and cons
      Leon Adato

      From what I've seen, WMI *does* pull interface stats. However, I have both NPM and SAM and it's possible some of what I'm seeing is coming from SAM rather than native NPM.

      • Re: SNMP vs WMI polling - pros and cons
        netlogix

        Another PRO for WMI is that it grabs the "Avg. Disk sec/Transfer", "Disk queue length", "Total Disk IOPS", and "Disk Allocation Failures" for volumes - never seen anything in "Disk Allocation Failures", but that a good thing right?

         

        I am not sure what version added that, but I was messing around with adding the new graphs and saw them and played around till I found that they had data if the server was WMI.

      • Re: SNMP vs WMI polling - pros and cons
        jeykfroze12

        I agree to Leon Adato, You must have both NPM and SAM.

         

        Here's the list resources of NPM only

        Screen Shot 2013-11-19 at 11.50.02 AM.png

         

        Here's the list resources after SAM installed (assuming you added application components of this server)

        Screen Shot 2013-11-19 at 12.36.27 PM.png

  • Re: SNMP vs WMI polling - pros and cons
    keithjen

    I’d like to see the option to use both SNMP and WMI methods.

    I monitor using SNMP across the board, but I want some of the options that WMI monitoring offers such as an account associated with the node (for service control via Solarwinds etc.)  and Disk Performance stats without needing to install “SNMP Informant Standard” on all my servers, or add  additional monitors manually.

    I’m not saying that the same info should be gathered by both methods. I’m sure that the bods at Solarwinds know which data is best pulled from SNMP and which from WMI? If not, they could give the admin the choice of setting one as the primary method.