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VSICM55 - Slide 11-22 - Removing a Host from the DRS Cluster



Wrong:

When describing the side effects of removing a host from a cluster, the second item if the bulleted list in the slide notes states:

Virtual machines with disks on local storage must be powered off, suspended, or migrated to another host and datastore by using EVC.
Correct:

EVC - Enhanced vMotion Compatibility - is something completely different from what you need here to migrate virtual machines either to a different host or to another datastore.

This is a typo, likely caused by a "search & replace" task with the text editor. The author, here, very likely wanted to say Enhanced vMotion (hence the typo while shortening the term), which has been now renamed into Cross-Host vMotion in vSphere 5.5.


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VSICM55 - Slide 11-19 - Viewing DRS Recommendations



Wrong:

When describing the vSphere DRS tab, the first paragraph in the slide notes states:

The DRS tab displays information about the DRS recommendations made for the cluster, the faults that have occurred in applying such recommendations, and the history of DRS actions. You can access three views from the DRS tab: Recommendations, Faults, and History.
Correct:

If you look at the vSphere Web Client, which is show in the slide graphic, elements names in the GUI are different than those mentioned above. Hence, the paragraph should be amended as follows:

The vSphere DRS link under the Monitor tab for the cluster displays information about the DRS recommendations made for the cluster, the faults that have occurred in applying such recommendations, and the history of DRS actions. You can access three views from the vSphere DRS tab: Recommendations, Faults, and History.

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VSICM55 - Slide 11-12 - DRS Cluster Settings: DRS Groups



Wrong:

The last sentence in the second paragraph of the slide notes states:

On the slide, Blade Chassis A, Blade Chassis B, and ISV-Licensed are host DRS groups.
Correct:

This description refers to something that is actually not displayed anywhere in the slide. This sentence is a leftover from previous editions of this course.


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VSICM55 - Slide 11-09 - EVC Cluster Requirements



Room for improvement:

While describing the CPU vendors' supporting technologies for EVC, the second sentence in the slide notes states:

EVC automatically configures hosts whose CPUs feature Intel FlexMigration and AMD-V Extended Migration technologies to be compatible with vSphere vMotion with hosts that use older CPUs.
Correct:

The actual complete Intel's marketing name for the technology is Intel VT FlexMigration.

Source:

VMware White Papers.


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VSICM55 - Slide 11-07 - Other Cluster Settings: EVC for DRS



Wrong:

While describing how to enable EVC, the first sentence in the slide notes states:

In the VMware EVC section of the New Cluster dialog box, you can enable Enhanced vMotion Compatibility (EVC).
Correct:

In the vSphere Web Client, shown in the slide graphic, the mentioned section is actually called EVC only.


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VSICM55 - Slide 11-06 - DRS Cluster Settings: Automation Level



Wrong:

While describing how to enable vSphere DRS, the first paragraph in the slide notes states:

Type a descriptive name for your cluster and select the Turn On VMware DRS check box.
Correct:

In the vSphere Web Client, shown in the slide graphic, the mentioned check box is actually called Turn On only and is available within the DRS section.


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VSICM55 - Slide 10-42 - Failed Master Host



Wrong:

While describing the master host election process, slide notes state:

If all slave hosts have equal datastore access, the election process selects a new master host using the highest numbered managed object ID (MOID) assigned by vCenter Server when the host was added to the vCenter Server inventory.
Correct:

Actually, according to Duncan Epping's article "HA Deepdive" on his blog Yellow-Bricks:

If two or more hosts have the same number of datastores connected, the one with the highest Managed Object Id will be chosen. This however is done lexically; meaning that 99 beats 100 as 9 is larger than 1.
Info:

Duncan Epping is - taking his self-description on his Twitter account (@DuncanYB) as of the day of the publication of this article - "Principal Architect @ VMware R&D. Start-up Advisor. Author of virtualization blog yellow-bricks.com. Author of vSphere Clustering Deepdive. Runner".

Source:

www.yellow-bricks.com


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VSICM55 - Slide 10-39 - vSphere HA Architecture: Datastore Heartbeats



Ambiguous:

The first sentence in the slide notes states:

Datastores are used as a backup communication channel to detect virtual machine and host heartbeats.
Correct:

The highlighted portion of the above sentence is very ambiguous. To me, it seems to imply that the virtual machines heartbeat mechanism (provided by the VMware Tools) can failover to a datastore heartbeat-like capability.
This is - AFAIK - a nonsense because:

  • Virtual machine heartbeats are "raised" by the VMware Tools in the guest OS and "catched" internally by hostd in the ESXi host running that VM, without using the network. Thanks to this capability, virtual machine heartbeats - and VM Monitoring, in vSphere HA - work with any VM, regardless there is a configured vNIC or not.
    As there is no networking resource failing here, there is also no need to have a backup mechanism based on the datastore(s).
  • I've never heard anything about such a feature anywhere, neither on the official VMware documentation, nor from any VCDX's or vExpert's blog, not even a rumor since when virtual machines heartbeats where introduced ages ago.
    The above mentioned sentence is likely to be simply a misleading statement.
Possible interpretation:

In vCenter Server 4.0, VMware introduced an additional disk I/0 status check, after the virtual machine heartbeat fails, to prevent accidental VM resets. This check ensures to wait for 120 seconds (by default) of no disk I/O activity before the reset takes place. The das.iostatsInterval advanced HA attribute can further customize the time the host is going to wait before actually resetting the VM.
This disk I/0 status check might be what the slide notes are referring to as "a backup communication channel to detect virtual machine heartbeats".

Source:

VMware Knowledge Base articles.


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VSICM55 - Slide 10-27 - vSphere HA Settings: Datastore Heartbeating



Room for improvement:

When describing the Datastore Heartbeating failure detection mechanism, slide notes provide a slightly messy statement:

Using datastore heartbeating, the master host determines whether the other host has failed, is part of a network partition, or network isolation has occurred. If datastore heartbeating from the host stops, then the host considers the host failed.
Correct:

For clarification, the highlighted sentence might be re-worded as follows:

If datastore heartbeating from the host stops, then the master host considers that host failed.

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