• Skip to primary navigation
  • Skip to main content
  • Skip to primary sidebar

Yellow Bricks

by Duncan Epping

  • Home
  • ESXTOP
  • Stickers/Shirts
  • Privacy Policy
  • About
  • Show Search
Hide Search

HA slotsize caveat…

Duncan Epping · Jul 21, 2011 ·

I had a question this week from one of my colleagues which had me dazzled for a while. A customer had an HA enabled cluster and used “Host Failures Cluster Tolerates” as the admission control policy. As you hopefully all know it uses a slot algorithm, in short:

HA uses the highest CPU reservation of any given VM and the highest memory reservation of any given VM. If no reservations of higher than 256Mhz are set HA will use a default of 256Mhz for CPU and a default of 0MB+memory overhead for memory.

In their case they ended up with a slot size of 405MB. However after validating the overhead of all machines they found that the largest memory overhead was 149MB. So where did this 405MB come from? Luckily one of the engineers responded to the email thread and managed to clear things up. With vCenter 2.5 we also used a default slotsize of 256MB for memory. This default slotsize is configured in “vpxd.cfg” and unfortunately after upgrading from 2.5 to vCenter 4.0 this setting is not reset. For this customer that meant that the result was:

256 (default slotsize) + 149 (dynamic memory overhead) = 405MB

Although a minor issue, definitely something to keep in mind when troubleshooting HA slotsize issues. Always check the vpxd.cfg and check if there are any values defined for “<slotMemMinMB>”.

Share it:

  • Tweet

Related

Server 4.1, ha, vSphere

Reader Interactions

Comments

  1. Linus B. says

    25 July, 2011 at 07:04

    Just to be clear, it should have been 0+overhead but it wasn’t because of the upgrade from 2.5?

    • Duncan says

      25 July, 2011 at 08:37

      That is correct. Although the “default behavior” changed this was only for newly installed environments as the installer did not change the setting.

  2. Shane says

    11 August, 2011 at 14:45

    Duncan,
    I’ve always had a question about the slot size algorhithm. Could you clarify or point me in the right direction for clarification? My question: why is it that HA uses the highest CPU reservation of “any given VM” and the highest memory reservation of “any given VM”, and not ALL VMs in the cluster? Doesn’t the remaining host in the cluster (or hostS) need to have enough resources for ALL VMs, and not just the ones that are powered on, more specifically, a VM with the highest CPU Res and Mem Overhead?

    Thanks.

Primary Sidebar

About the author

Duncan Epping is a Chief Technologist in the Office of CTO of the Cloud Platform BU at VMware. He is a VCDX (# 007), the author of the "vSAN Deep Dive", the “vSphere Clustering Technical Deep Dive” series, and the host of the "Unexplored Territory" podcast.

Upcoming Events

29-08-2022 – VMware Explore US
07-11-2022 – VMware Explore EMEA
….

Recommended Reads

Sponsors

Want to support Yellow-Bricks? Buy an advert!

Advertisements

Copyright Yellow-Bricks.com © 2022 · Log in