I just ran into an issue for a customer that is running vCenter 5.5.  Apparently, there is a known issue with the 5.5 version of the syslog collector that causes the debug log to grow indefinitely when it was upgraded  to 5.5 according to the article.  However, the customer in question was built fresh with 5.5, although I did update within 5.5 to newer builds during that time.  Bottom line is it should be checked if they’re running 5.5 version of the syslog collector in all cases to be sure.  The KB article outlines steps to stop this, which basically involves turning off debug logging altogether.

The debug log doesn’t contain actual syslog info for hosts, so this log file is only useful for troubleshooting issues with the syslog collector itself, so it’s almost certainly safe to delete.

Please note this only impacts the syslog collector.  If you did not install the syslog collector, this isn’t applicable.

You can copy and paste the following into an admin elevated PowerShell window to automate stopping the syslog service, changing the config file for the syslog collector to turn off debug logging completely, delete the probably massive debug log, and start the syslog collector again.  You can also save it as a .ps1 file and run it in an elevated prompt as well.

stop-service vmware-syslog-collector
(get-content "C:\ProgramData\VMware\VMware Syslog Collector\vmconfig-syslog.xml") | foreach-object {$_ -replace "<level>1</level>", "<level>0</level>"} | set-content "C:\ProgramData\VMware\VMware Syslog Collector\vmconfig-syslog.xml"
remove-item "C:\ProgramData\VMware\VMware Syslog Collector\logs\debug.log"
start-service vmware-syslog-collector

This assumes of course the syslog collector is running on a Windows machine, not the vCenter Appliance.  The article doesn’t seem to make clear if this issue only applies to the Windows version of Vcenter, and how to fix the vCenter Appliance if the issue did impact it as well.

Hope this helps!