In VMware infrastructure we have still seen pushing on the limits. One of the limit which we have to take into account is heap size. Particulary if you are in the middle of project of migration of all oracle database to virtual infastructure with couple of TB disks. Default value for vSphere 5.0 for VMFS3.MaxHeapSizeMB is 80MB what in summary gets us up to 8TB of vmdks per esxi host. If you hit this limit you will not able to power on VMs. You can change this value to max. 256MB but it required esxi host to reboot. Imagine situation where you finished migration you have enough CPU and memory but you are not able power on DB because you forget increase heap size, and all previously migrated VMs are in production. If you lucky emogh you can shuffle VMs between hosts to bypass and fit to 8TB limit.
Here is VMware kb article:
http://kb.vmware.com/kb/1004424
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