Information
Configure persistent logging for all ESXi host.
ESXi can be configured to store log files on an in-memory file system. This occurs when the host's "/scratch" directory is linked to "/tmp/scratch". When this is done only a single day's worth of logs are stored at any time. In addition log files will be reinitialized upon each reboot. This presents a security risk as user activity logged on the host is only stored temporarily and will not persistent across reboots. This can also complicate auditing and make it harder to monitor events and diagnose issues. ESXi host logging should always be configured to a persistent datastore.
http://kb.vmware.com/kb/1033696
http://pubs.vmware.com/vsphere-65/topic/com.vmware.vsphere.security.doc/GUID-9F67DB52-F469-451F-B6C8-DAE8D95976E7.html
Solution
# Set Syslog.global.logDir for each host
Get-VMHost | Foreach { Set-VMHostAdvancedConfiguration -VMHost $_ -Name Syslog.global.logDir -Value "NewLocation" }