In legacy versions of PVS, it was necessary that the administrator configure the pagefile settings in the image to redirect to the cache disk.  The cache disk is usually D:, but can be E: if, for example, there is a DVD drive.  The administrator was responsible for configuring the pagefile settings correctly for their image. Modern supported versions of PVS including all of 7.x detect if the pagefile was configured to be on the boot disk and recdirect it for the cache disk. At this time, the code was modified to ALWAYS assign a drive letter to the cache disk at early boot time and then it would update the registry to redirect the pagefile to this if necessary (it only does it if the pagefile in the image is configured to be on the boot disk).

Administrators who were used to setting the pagefile in the image didnt notice any changes, the early boot code would not change anything with the pagefile settings BUT would still assign a drive letter (usually D:) to the cache diisk, if assumed that the administrator had set the pagefile to whatever drive the cache ended up.  When we allocate a drive letter, we just pick the next available.

CVADHELP-28305

Support for Azure changed some of the PVS early boot code leading to a possible change in behavior for any legacy pagefile configurations, meaning if pagefile was redirected manually for the sake of streaming or some other purpose it may not take the machine configuration.   A fix has been created to adjust for any manual configuration and will be merged into new releses

Its recommend that the Administrator leave the pagefile on C: while creating the Master Target Device.  Citrix recommends leaving Pagefile set to Let Windows Manage for PVS, unless there is a third party requirement for something specific.  

Failure to redirect the pagefile at boot can result in Target performance problems, including Citrix VDA policies applying correctly and poor streaming performance.  Azure VM's may fail to be created due to BSOD while setting up the cache file.  A Target Device machine may boot and report no pagefile configured.