2V0-621 · Question #180
What are two likely causes for a DRS cluster to become unbalanced? (Choose two.)
The correct answer is B. Affinity rules are preventing virtual machines from being moved. C. A device is mounted to a virtual machine preventing vMotion.. A DRS cluster becomes persistently unbalanced when certain VMs cannot be migrated due to absolute constraints such as affinity rules or attached local devices that block vMotion.
Question
What are two likely causes for a DRS cluster to become unbalanced? (Choose two.)
Options
- AMigration threshold is too low.
- BAffinity rules are preventing virtual machines from being moved.
- CA device is mounted to a virtual machine preventing vMotion.
- DMigration cost is too low.
How the community answered
(30 responses)- A7% (2)
- B77% (23)
- D17% (5)
Why each option
A DRS cluster becomes persistently unbalanced when certain VMs cannot be migrated due to absolute constraints such as affinity rules or attached local devices that block vMotion.
A conservative (low) migration threshold reduces the frequency and priority of DRS recommendations but does not create an absolute migration block - it simply raises the imbalance severity required before a recommendation is issued.
VM-to-VM or VM-to-host affinity and anti-affinity rules can prevent DRS from issuing valid migration recommendations for specific VMs, leaving those VMs pinned to overloaded or underutilized hosts and causing a sustained imbalance in the cluster.
A locally attached device such as a connected CD-ROM, floppy, or USB passthrough device renders a VM ineligible for vMotion, so DRS cannot migrate it to rebalance load even when a significant imbalance exists.
Migration cost is an internal DRS calculation factor used to weigh the benefit of a migration against its overhead - it is not a standalone administrator-configurable setting and a low migration cost would encourage more migrations rather than prevent rebalancing.
Concept tested: DRS cluster imbalance causes - affinity rules and vMotion blockers
Source: https://docs.vmware.com/en/VMware-vSphere/7.0/com.vmware.vsphere.resmgmt.doc/GUID-DC70BF5D-8D5A-44AB-BF79-DEDAE9D42C98.html
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