Vcap-Dca Objective 3.2 – Optimize Virtual Machine Resources

Front 1

Identify VMware memory management techniques: Modifying attributes

Back 1

Resource Management, P 102

Advanced configuration of memory management is done via advanced host settings. From Inventory -> Hosts and Clusters

1. Select Host.
2. Click on Configuration tab.
3. Under Software click the Advanced Settings link.
4. When advanced settings comes up, click on the "Mem" group attribute.
5. In the right-hand pane, modify the Mem attribute and value required.

Front 2

Identify VMware memory management techniques: Working set size monitoring interval

Back 2

Resource Management, P 102

Hosts allocate memory to virtual machines based on their most recent working set size and relative shares to the resource pool. The working set size is monitored for 60 seconds. This interval can be changed by modifying the advanced host setting: Mem.SamplePeriod

Front 3

Identify VMware memory management techniques: Memory Sharing (TPS)

Back 3

Resource Management, P 102

Memory Sharing/Transparent Page Sharing (TPS)
Several virtual machines might be running instances of the same guest operating system, have the same applications or components loaded, or contain common data. In such cases, ESXi systems use a proprietary transparent page-sharing technique to securely eliminate redundant copies of memory pages. With memory sharing, a workload running in virtual machines often consumes less memory than it would when running on physical machines, and thus, higher levels of overcommitment can be supported efficiently.

There are two advanced hosts settings for TPS:

Mem.ShareScanTime - how often hosts scan for memory (default: 60 minutes)

Mem.ShareScanGHz - how much CPU resources are consumed in scan (default: 4)

Front 4

Identify VMware memory management techniques: Memory compression

Back 4

Resource Management, P 102

ESXi provides memory compression cache to improve virtual machine performance when you use memory overcommitment. Memory compression is enabled by default. When a host's memory becomes overcommitted, ESXi compresses virtual pages and stores them in memory.

Because accessing compressed memory is faster than accessing memory that is swapped to disk, memory compression in ESXi allows you to overcommit memory without significantly hindering performance. When a virtual page needs to be swapped, ESXi first attempts to compress the page. Pages that can be compressed to 2 KB or smaller are stored in the virtual machine's compression cache, increasing the capacity of the host.

There are two advanced hosts settings for Memory Compression:

Mem.MemZipMaxPct - maximum size of the compression cache (default 10%)

Mem.MemZipEnable - used to enable/disable memory compression (0 to disable)

Front 5

Identify VMware memory management techniques: Idle Memory Tax

Back 5

Resource Management, P 102

If a virtual machine is not actively using all of its currently allocated memory, ESXi charges more for idle memory than for memory that is in use. This is done to help prevent virtual machines from hoarding idle memory.

The idle memory tax is applied in a progressive fashion. The effective tax rate increases as the ratio of idle memory to active memory for the virtual machine rises.

There are two advanced hosts settings for Idle Memory Tax:

Mem.IdleTax - maximum percentage of total guest memory that can be reclaimed (default: 75%)

Mem.IdleTaxType - specifies whether tax increase/decreases based on the amount of idle memory, or is a flat rate (default is 1, which will set the tax rate to be variable; 0 will set it to a flat rate)

Front 6

Identify VMware memory management technique: Ballooning

Back 6

Resource Management, P 102

ESXi hosts can reclaim memory from virtual machines.

A host allocates the amount of memory specified by a reservation directly to a virtual machine. Anything beyond the reservation is allocated using the host's physical resources or, when physical resources are not available, handled using special techniques such as ballooning or swapping.

The memory balloon driver (vmmemctl) collaborates with the server to reclaim pages that are considered least valuable by the guest operating system.

The driver uses a proprietary ballooning technique that provides predictable performance that closely matches the behavior of a native system under similar memory constraints. This technique increases or decreases memory pressure on the guest operating system, causing the guest to use its own native memory management algorithms. When memory is tight, the guest operating system determines which pages to reclaim and, if necessary, swaps them to its own virtual disk.

There is only one advanced setting for Ballooning and it's configured on the virtual machine, not the host:

sched.mem.maxmemxtl- limit the amount of memory that gets reclaimed on a per-virtual machine basis (value specified in MB, with no default)

Front 7

Identify VMware memory management technique: Memory Swapping

Back 7

Resource Management, P 102

ESXi hosts can reclaim memory from virtual machines.

A host allocates the amount of memory specified by a reservation directly to a virtual machine. Anything beyond the reservation is allocated using the host's physical resources or, when physical resources are not available, handled using special techniques such as ballooning or swapping.

There are two types of swap to disk mechanism; swap to disk and swap to host cache.

For swap to disk, a swap file is created during power-on and during times of memory contention in the location of the virtual machine's configuration file (VMX).

Alternatively, you can set the swap file location to a datastore and change the location per-VM, per-host, or per-cluster.

Front 8

Enable Host-Local Swap for a DRS Cluster

Back 8

Resource Management, P 35

From Inventory -> Hosts and Clusters.

1. Right-click on the Cluster and select Edit Settings
2. Click Swapfile Location.
3. Select "Store the swapfile in the datastore specified by the host"
4. Click OK
5. Select a Host.
5. Click the Configuration tab.
7. Under software, select Virtual Machine Swapfile Location.
8. Click Edit
9. Select Store the swapfile in the swapfile datastore.
10. Select a local datastore from the list and click OK.

Front 9

Identify VMware CPU load balancing techniques: General

Back 9

ESXi hosts can take advantage of multicore processors. By default, the CPU scheduler will spread the workload across all sockets in the system in undercommitted systems.

You can override the default behavior by adding: sched.cpu.vsmpConsolidate=True to the virtual machine configuration file. This setting will prevent the workload from being spread across all sockets and limit it to the same socket.

Front 10

Identify VMware CPU load balancing techniques: hyper-threading

Back 10

Resource Management, P 20

Hyper-threading needs to be enabled in the BIOS and once that is done, should automatically be enabled in vSphere.

Be careful when setting manual affinity when hosts have hyper-threading enabled. Two virtual machines may get bound to the same core which could be detrimental to the performance of those workloads.

Front 11

Identify VMware CPU load balancing techniques: NUMA (Non-Uniformed Memory Access)

Back 11

Resource Management, P 20

NUMA is an architecture that provides more than one memory bus. Each socket has its own bus to memory and the physical processors have the option to access memory that isn't located on its dedicated bus (that's the non-uniform part).

When a virtual machine is allocated memory, it takes memory "locality" into consideration, meaning it will provide best effort in assigning memory that is from the home node (the home node is a term used to describe a processor and memory local to that processor)

If there is an imbalance in the load, the NUMA scheduler can change a virtual machine's home node on the fly. Even though the home node moves to a new home node, it does not automatically mean that the memory is relocated to its new home node. The scheduler has the ability to relocate memory to once again make it local.

The dynamic load balancing algorithm will examine the load and decide whether a rebalance is needed, this happens every two seconds by default.

Front 12

Identify prerequisites for Hot Add features

Back 12

Virtual Machine Administration, pages 90 - 92 (CPU), pages 103 - 104 (memory)

Only certain guest operating systems are supported for Hot Add, so ensure the guest operating system you are using supports it.

Hot Add must be enabled per virtual machine and the virtual machine must be powered off in order to enable it.

If you are hot-adding multicore vCPUs then the virtual machine must be using hardware version 8.

If you are hot-adding a vCPU to a virtual machine using virtual hardware 7, the number of cores per socket must be set to 1.

The virtual machine MUST have at least hardware version 7 or later.

Install VMware Tools

Front 13

Tune virtual machine memory configurations

Back 13

Virtual Machine Administration, Pp 36 - 37

Pay attention to your virtual machine memory allocation. You don't want to overcommit to the point where the VM starts swapping to host cache, or worse, disk. You can use the built-in performance charts and esxtop to determine whether the VM is swapping pages to virtual disk or the host is swapping to disk.

Don't oversize memory on your virtual machines. Even if you have the available physical memory, don't allocate any more than what's needed. Over-allocating memory will waste physical memory as the more memory you allocate to the virtual machine, the more memory the vmkernel takes for overhead.

Proceed cautiously when setting memory reservations and limits. Setting these too low or too high can cause unnecessary memory ballooning and swapping.

Ensure VMware Tools is installed and up-to-date.

If you need to control priority over memory, use memory shares to determine relative priority.

Use an SSD to configure host cache.

Front 14

Tune virtual machine networking configurations

Back 14

Virtual Machine Administration, page 35

Use the paravirtualized network adapter, also known as the VMXNET3 adapter.
-Requires VMware tools to be installed.
-Requires virtual machine hardware version 7 or later.

Ensure jumbo frames for the VM if the rest of the infrastructure is using jumbo frames (set in the Guest OS driver).

Front 15

Tune virtual machine CPU configurations: hyper-threading

Back 15

Virtual Machine Administration, page 34

If hyperthreading is enabled for the host, ensure that the Hyperthreaded Core Sharing Mode for your virtual machines is set to "Any"

If you need to disable hyper-threading for a particular virtual machine, set the Hyper-threaded Core Sharing Mode to "None"

To do this, from Inventory -> Hosts and Clusters

1. Select the VM
2. Click Edit Settings
3. Click on the Resources tab.
4. Click on Advanced CPU
5. Under Advanced CPU, change the Hyperthreaded Core Sharing Mode using the drop-down box.
6. Click OK.

Front 16

Tune virtual machine CPU configurations: HAL

Back 16

Virtual Machine Administration, page 34

Select the proper Hardware Abstraction Layer (HAL) for the guest operating system you are using.

-This only applies for the guest operating systems that have different kernels for single processor (UP) and multiple processors (SMP). Single vCPU would use UP and all others will use SMP.

If your application or guest OS can't leverage multiple processors then configure them with only 1 vCPU.

Front 17

Tune virtual machine CPU configurations: NUMA

Back 17

Virtual Machine Administration, page 34

If your physical hosts are using NUMA, ensure the virtual machines are hardware version 8 as this exposes the NUMA architecture to the guest operating systems, allowing NUMA aware applications to take advantage of it.

Front 18

Tune Virtual Machine storage configuration

Back 18

Virtual Machine Administration, pages 36-38

Logical disks you create inside the guest OS should be separated into separate VMDK files. In other words, have a 1:1 for logical disks and VMDKs for your OS disk and data disks.

Ensure the guest operating system disks are aligned with the VMFS volumes they reside on. Newer guest operating systems (such as Windows Server 2008) do this automatically.

Consider using the paravirtualized SCSI (PVSCSI) adapter.
-The PVSCSI adapter can provide higher throughput and lower CPU utilization.
-Requires virtual machine hardware version 7 or later.

Large I/O requests have the potential to be broken up into smaller requests by the device driver within the guest OS. Modify the registry to increase the block size as fragmented I/O requests can reduce performance.

Front 19

Calculate Available Resources: Calculate Cluster Resources

Back 19

Resource Management, pages 9 - 11

From Inventory -> Hosts and Clusters

1. Select a cluster.
2. Click the Summary tab.
3. In the right-hand pane of the summary tab, under vSphere DRS, click View Resource Distribution Chart.

Front 20

Calculate Available Resources: Calculate Host Resources

Back 20

Resource Management, pages 9 - 11

From Inventory -> Hosts and Clusters

1. Select a host.
2. Click the summary tab.
3. Under Resources, both CPU and memory usage are displayed.

Front 21

Calculate Available Resources: Calculate Virtual Machine Resources

Back 21

Resource Management, pages 9 - 11

From Inventory -> Hosts and Clusters

1. Select a virtual machine.
2. Click the Resource Allocation tab.

Front 22

Calculate Available Resources from ESXTOP: CPU Metrics

Back 22

Resource Management, Pp 9 - 11

Run esxtop.
CPU is the default view (option 'c')

CPU metrics of note:
% USED - percentage of physical CPU core cycles used by a group of worlds (resource pools, running VMs, etc).

%SYS - percentage of time spend in the vmkernel processing requests.

%RDY - percentage of time the group was ready to run but inadequate CPU resources were available to handle the request.

%WAIT - percentage of time the group was in a clock or wait state (includes idle time)

You can also enter 'v' to display VM specific metrics. %USED provides a good indication of CPU resources available to service the VM's requests.

Front 23

Calculate Available Resources from ESXTOP: Memory Metrics

Back 23

Resource Management, Pp 9 - 11

Run esxtop.
Change to memory view (option 'm')

Memory metrics of note:
PMEM/MB - the total amount of physical memory installed in the ESXi host.
The "total" value represents the amount of memory that is actively being used by the host.
"vmk" indicates how much memory is actively being used by the vmkernel.
"free" displays how much free host memory is available to service requests.

VMKMEM/MB - includes rsvd and ursvd, which reflect how much host memory is reserved and unreserved.

Enter 'v' to display VM specific memory metrics.

Front 24

Modify large memory page settings

Back 24

Resource Management Guide, page 100

From Inventory -> Hosts and Clusters

1. Select a host.
2. Click the configuration tab.
3. Under software, click the Advanced Settings link.
4. 4. Click the LPage attribute group on the left and find the setting you want to modify.

Front 25

Understand appropriate use cases for CPU affinity

Back 25

Some use cases for CPU affinity:
Simulating a workload
Load testing for an application

Potential issues with CPU affinity:

If you are using NUMA hardware, the NUMA scheduler may not be able to manage virtual machines with CPU affinity, essentially disabling NUMA for that virtual machine.

Hyperthreading enabled hosts may not be able to fully leverage hyperthreading on a virtual machine with CPU affinity.

Reservations and shares may not be fully respected for a virtual machine configured for CPU affinity.

Front 26

Set CPU Affinity

Back 26

From Inventory -> Hosts and Clusters

1. Select a VM.
2. Click Edit Settings
3. Click on the Resources tab.
4. Select Advanced CPU.
5. Under scheduling affinity, specify the physical processor (core) or ranges of cores available on the ESXi host.
6. Click OK.

Front 27

Configure alternate virtual machine swap locations: configure cluster swap settings

Back 27

From Inventory -> Hosts and Clusters

1. Select cluster.
2. Right-click and select Edit Settings.
3. Click on Swapfile Location
4. Choose to Store the swapfile in the datastore specified by the host.
5. Click OK.

Front 28

Configure alternate virtual machine swap locations: configure host swap settings

Back 28

From Inventory -> Hosts and Clusters

1. Select host
2. Click on Configuration tab.
3. Under software, click on Virtual Machine Swapfile Location.
4. Click on Edit
5. Select Store the swapfile in the swapfile datastore.
6. Select a datastore from the list and click OK.

Front 29

Configure alternate virtual machine swap locations: configure per-VM swapfile location

Back 29

From Inventory -> Hosts and Clusters

1. Select VM.
2. Select Edit Settings
3. Click the Options tab.
4. Select swapfile location.
5. Select one of the following locations:

Default - either the cluster default or the host default

Always store with the virtual machine - swapfile is stored in the same directory as the virtual machine configuration file.

Store swap file in the host's swapfile directory