VCAP-DCA Study notes 6.2 – Troubleshoot CPU and Memory Performance

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Knowledge

  • Identify resxtop/esxtop metrics related to memory and CPU
  • Identify vCenter Server Performance Chart metrics related to memory and CPU

Skills and Abilities

  • Troubleshoot ESX/ESXi Host and Virtual Machine CPU performance issues using appropriate metrics
  • Troubleshoot ESX/ESXi Host and Virtual Machine memory performance issues using appropriate metrics
  • Use Hot‐Add functionality to resolve identified Virtual Machine CPU and memory performance issues

Tools & learning resources

This is another objective that’s hard to quantify – experience will be the main requirement! There are some great general purpose resources out there;

Note that resxtop (built in to the vMA) does not offer the ‘replay’ mode available in ESX classic. Source: VMworld session MA6580, vMA Tips and Tricks.

Identify esxtop and vCenter metrics related to memory and CPU

See section 3.1 in the Performance chapter for a list of metrics to check.

Troubleshoot ESX/ESXi host and VM memory performance issues using appropriate metrics

Read the ESXTOP bible which covers metrics to look for and typical values for various problems.

Remedial actions

  • Verify that VMtools is installed in every VM (otherwise the balloon driver won’t be active and swapping will occur)
  • Verify that the balloon driver is active (look for MCTL? in esxtop)
  • Check for resource limits or insufficient reservations (both on the VM and any resource pools)
  • If the host is in a cluster, enable DRS if not already enabled
  • Check for VMs with a high reservation (compared to active memory). This may be a sign that the VM is oversized and memory is being wasted (be careful with Java and Oracle)
  • Add more physical memory to the host

NOTE: On Xeon 5500 (Nehalem) hosts TPS won’t show much benefit until you overcommit memory (assuming you use large memory pages in both the guest OS and ESX (VMwareKB1021095)

NOTE: vim-cmd is only available on ESXi and ESX hosts but NOT in the vMA.

Troubleshoot ESX/ESXi host and VM CPU performance issues using appropriate metrics

Read the ESXTOP bible which covers metrics to look for and typical values for various problems.

Remedial actions

For clusters

  • enable DRS if not already enabled. This may alleviate hotspots.
  • If DRS is already enabled
    • add hosts
    • check threshold setting. Setting a higher threshold may balance load more effectively.

For all hosts

  • Enable CPU saving features such as TSO, h/w iSCSI initiators, TSO enabled pNICs, large memory pages, newer vNIC drivers (VMXNET3) etc
  • Ensure VMtools is enabled in all VMs
  • Right size VMs which are incorrectly allocated vSMP for single threaded apps

Use Hot-Add functionality to resolve identified VM CPU and memory performance issues

Covered in section 3.1

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