was I think quoted earlier by a respondent. It gives fairly clear guidelines:
ESX hosts store all files necessary for virtual machine operation in a VMware Virtual Machine File System (VMFS). Proper capacity management is critical because this file system is required for any operations related to a virtual machine. This document outlines potential issues related to a VMFS becoming full.
All VMFS (vmfs2, vmfs3, vmfs5) must retain a level of free space to ensure that the virtual machine functions properly. Ensure that these capacity thresholds are met:
200 Megabyte Capacity: VMware suggests 200 MB as the threshold where ESX system administrators take action to resolve capacity issues. VMFS volumes vary widely in size and it is impossible to define a precise percentage, but the risk of unexpected problems become greater at this point.
100 Megabyte Remaining: If left unchecked, a VMFS volume grows until only 100 MB of space remains, at which time issues may occur. 100 MB is defined as a critical threshold at which ESX system administrators must take immediate action to correct the issue because VMware VMFS stops growing at this point.
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"I like flaws and feel more comfortable around people who have them. I myself am made entirely of flaws, stitched together with good intentions."
Augusten Burroughs