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An ESX host reports vmfs heap warnings when hosting virtual machines that collectively use 4TB of virtual disk storage

Symptoms

ESX host has more that 4 terabytes (TB) of virtual disks (.vmdk files) open.
Warnings similar to the following are found in /var/log/vmkernel or the /var/log/messages log:

vmkernel: 8:18:59:58.640 cpu2:1410)WARNING: Heap: 1370: Heap_Align(vmfs3, 4096/4096 bytes, 4 align) failed. caller: 0x8fdbd0
vmkernel: 8:18:59:58.640 cpu2:1410)WARNING: Heap: 1266: Heap vmfs3: Maximum allowed growth (24) too small for size (8192)

Purpose

This article addresses the issue of running out of heap space on an ESX host when a large quantity is virtual disk space is active.

Resolution

The default heap size in ESX 3.5/4.0 for VMFS-3 is set to 16MB. This allows for a maximum of 4TB of open virtual disk capacity on a single ESX host. The default heap size has been increased in ESX 4.1 to 80M, which allows for 20TB of open virtual disk capacity on a single ESX host.

To adjust the value:

Log in to vCenter Server or the ESX host using VMware Infrastructure (VI) Client. If connecting to vCenter Server, select the ESX host from the inventory.
Click the Configuration tab.
Click Advanced Settings.
Select VMFS3.
Update the field in VMFS3.MaxHeapSizeMB.

Note: The maximum heap size is 128MB. This allows a maximum of 32TB of open storage.
Reboot the ESX host for the changes to take affect.

Additional Information

This article does not apply to ESXi 5.x, if you are using VMFS-3 on the ESXi 5.x host.
However this issue can occur on ESXi 5.0 if you are using a VMFS5 datastore which has been converted from VMFS3.
In ESX 3.0, the VMFS3.MaxHeapSizeMB value cannot be modified.
In ESX 4.1, by default, the VMFS3.MaxHeapSizeMB option is set to 80MB. This value can be modifed and set to a value between the range of 16MB to 128MB. A higher value increases the threshold at which these warnings are reported.

Update History

11/28/2011 - Updated the Additional Information section

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