It demonstrated that by using DRS advanced options, we are able to balance memory usage across a cluster. In my next blog post, I examine memory consumption (usage) vs active memory (demand); and discuss the importance of understanding the difference and the impact on workload placement.
Key Terms
Active (Demand) - Amount of memory that is actively used, as estimated by the VMkernel based on recently touched memory pages.
- Virtual machine: Amount of guest “physical” memory actively used.
- Host: Sum of all active metrics for all powered-on virtual machines plus
services (such as COS,vSphere ) on the host.vpxa
Granted - The amount of machine memory or “physical” memory that is mapped for a virtual machine or a host.
- Virtual machine: Guest “physical” memory that is mapped to machine memory. Includes shared memory amount. Does not include overhead.
- Host: Sum of all granted metrics for all powered-on virtual machines, plus machine memory for
services on the host.vSphere
Consumed - Amount of memory consumed by a virtual machine, host, or cluster.
- Virtual machine: Amount of guest physical memory consumed by the virtual machine for guest memory. Consumed memory does not include overhead memory. It includes shared memory and memory that might be reserved, but not actually used. Use this metric for charge-back purposes.
consumed memory = memory granted - memory saved due to memory sharingvm - Host: Amount of machine memory used on the host. Consumed memory includes Includes memory used by the Service Console, the VMkernel,
services, plus the total consumed metrics for all running virtual machines.vSphere
consumed memory = total host memory - free host memoryhost
Usage - Memory usage as percentage of total configured or available memory.
- Virtual machine: Percentage of configured virtual machine “physical” memory.
÷ virtual machine configured sizeactive - Host: Percentage of available machine memory.
÷ machine-memory-sizeconsumed
Idle – Consumed memory that is not actively used.
DRS Migration Thresholds – The threshold set to automatically migrate virtual machines from one host to another to optimize resource usage.
- Level 1 – Apply only priority 1 migrations,
will only apply recommendations that must be taken to satisfy cluster constraints like affinity rules and host maintenance.vCenter - Level 2 – Apply priority 1 and 2 migrations,
will apply recommendations that promise a significant improvementvCenter theto load balance.cluster’s - Level 3 (default) – Apply priority 1, 2, and 3 migrations,
will apply recommendations that promise at least good improvement to thevCenter load balance.cluster’s - Level 4 - Apply priority 1, 2, 3, and 4 migrations,
will apply recommendations that promise even a moderate improvementvCenter theto load balance.cluster’s - Level 5 -
will apply recommendations that promise even a slight improvement to thevCenter load balance.cluster’s