Which log file would you examine to identify an issue which occurred during the pre-upgrade phase of a
vCenter Server upgrade process?

A.
vcdb_req.out

B.
vcdb_export.out

C.
vcdb_import.out

D.
vcdb_inplace.out

Explanation:

The vcdb_req.err file tracks any errors that were identified during the pre-upgrade phase.
Reference: http://pubs.vmware.com/vsphere-60/index.jsp?topic=%2Fcom.vmware.vsphere.upgrade.doc%
2FGUID-5EAC8B84-0A95-41EC-AAF4-6CBBB3A5152A.html