Yellow Bricks

by Duncan Epping

HA: Did you know?

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Did you know that…

  • the best practice to increase the isolation response time(das.failuredetectiontime) from 15000 to 60000 for an Active/Standby situation for your service console has been deprecated as of vSphere.
    (In other words for active/standby leave it set to the default 15000 for vSphere)
  • the limit of 100 VMs per host is actually “100 powered on and HA enabled VMs”. Of course this also goes for the 40 VM limit  for clusters with more than 8 hosts.
  • the limit of 100VMs per host in an HA cluster less than 9 hosts is a soft limit.
  • das.isolationaddress[0-9] is one of the most underrated advanced settings.
    It should be used as an additional safety net to rule out false positives.

Just four little things most people don’t seem to realize or know…

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Comments

  2. defuseme2k says

    OK, two things confuse me about the way you’ve stated this. I’m sure it has more to do with me than you, but just so I’m clear…

    “the limit of 100 VMs per host is actually “100 powered on and HA enabled VMs”. Of course this also goes for the 40 VM limit for clusters with more than 8 hosts.”

    The above looks like you’re saying if I had over 8 hosts, I can only have 40VMs per host that are powered on and HA enabled. That doesn’t sound right…

    “das.isolationaddress is one of the most underrated advanced settings.
    It should be used as an additional safety net to rule out false positives.
    It’s there for a reason, start using is… And if you do add 5 seconds to “das.failuredetectiontime””

    The above here is confusing as well. I’m still on 3.5, so I’ll ignore the 15000 vs 60000 since the latter is still true for me. However, if I had a second isolationaddress, I would want to make mine 65000, or for those with vSphere, theirs should be 20000 rather than 15000, correct?

  3. Duncan says

    @ian – 15000 is the default

    @defuseme2k
    1) check the max config guide. If a cluster has more than 8 hosts HA only supports a max of 40 VMs per host. However this is “running” and “HA Enabled” VMs per host.

    2) Correct, for vSphere that would be 20000. For 3.5 theoretically it should 65000 but I would say 600000 is more than sufficient.