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Poor performance while deploying virtual machines over the network (2052302)

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Symptoms

When attempting to deploy virtual machines over the network (where the virtual machines are not located on the shared storage), you experience these symptoms:
  • The deployment takes an excessive amount of time. This also includes deployment from vRealize Automation (formerly known as vCloud Automation Center) as well as vCloud Director (vCD).
  • Deploying virtual machines from a shared storage completes much sooner.
  • In the /var/log/vmkernel.log log file, you see Buffer Cache exhaustion errors similar to:

    BC: 3115: Blocking due to no free buffers. nDirty = 62 nWaiters = 1

Cause

When deploying virtual machines located on a non-shared storage to other ESXi hosts, the deployment occurs across the network (using NFC/hostd). This mayhave an impact on the file system buffer cache and exhaust the number of buffers, reporting significant delay in deployment time.

Resolution

To prevent this issue, relocate the virtual machine templates to a shared storage that is presented to all ESXi hosts.

To workaround this issue, increase the number of buffers and reduce the flush interval.

Note: ESXi 5.0 hosts must be running Update 2 or later, prior to applying this workaround.
 
To increase the number of buffers and reduce the flush interval:
  1. Log in to the Local Tech Support Mode console of the ESXi host. For more information, see Using Tech Support Mode in ESXi 4.1 and ESXi 5.x (1017910).
  2. To increase the number of buffers from 2048 to 4096, run this command:

    # esxcfg-advcfg -s 32768 /BufferCache/MaxCapacity

    Note: If the above change does not result in a significant improvement, try reducing the flush interval.

  3. To reduce the Buffer Cache Flush interval from 30 seconds to 20 seconds, run this command:

    # esxcfg-advcfg -s 20000 /BufferCache/FlushInterval
Notes:
  • You may continue to experience some buffer cache exhaustion on large virtual machines, but the frequency is usually much lower.
  • A host reboot is not required to increase the buffers, but to decrease the buffers to a lower value or to the default value, a host reboot is necessary for the changes to take effect.

See Also

Request a Product Feature

To request a new product feature or to provide feedback on a VMware product, please visit the Request a Product Feature page.

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