When you remove a virtual disk device (VHD or VHDx file) in Windows 8.1 or Windows Server 2012 R2, extraneous log entries that resemble the following are created:
Log Name: System
Source: disk
Date: <Date><Time>
Event ID: 157
Task Category: None
Level: Warning
Keywords: Classic
Computer: <Computer_name>
Description: Disk n has been surprise removed