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November 18, 2008


VMFS out of heap memory

The default heap size for VMFS-3 is set to 16Mb. This allows for a maximum of 4Tb of open virtual disk capacity on a single ESX host.

In ESX 3.0, the value cannot be adjusted. VMware is considering a patch to correct the issue.

In ESX 3.5, the value can be adjusted:

  1. Log in to the VirtualCenter or the ESX host using the Virtual Infrastructure Client. If connecting to VirtualCenter, select the ESX host from the inventory.
  2. Select the Configuration tab.
  3. Select Advanced Settings.
  4. Select VMFS3.
  5. Update the field in VMFS3.MaxHeapSizeMB.

The maximum heap size is 128Mb. This allows a maximum of 32Tb of open storage.

Applies to: VMware ESX 3.x

Read more from VMware
2 Comments Post a comment
  1. Feb 16 2011

    Note that this value is calculated for a VMFS block size of 1MB.
    In ESX 4.1 heap-size is now set to 80MB, which allows for 20TB of open virtual disk capacity on a single ESX host, but usually vAdmins format their datastores with 8MB block size which in turn allows only 2.5TB (20/8) of open virtual disk capacity…


  2. Chris
    Feb 16 2011

    Yeah, this was one of my old discoveries back when we were on ESX3. I figure that there are still some folks running it out there, so maybe it’ll help ’em out. vSphere 4 is definitely the best solution…


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