Persistent Drive
The native persistent drive is an important concept in Host Provisioning Services that helps you keep the data that you need to preserve between updates.
When a new updated vDisk is deployed to clients, the current running disk is wiped out when the client applies the new base or differencing disk, the way to preserve data is redirecting it to the persistent drive.
All files in the persistent drive are kept between updates.
Host Provisioning Client stores VHDx files, branchcache, logs and other configuration in the persistent drive.
A useful configuration in Computer Groups is fixing the permanent drive to a drive letter, for example "N:". This allows you to use the persistent drive in scripts, group policies or program's configuration using the fixed drive letter to store your data.
Depending on the type of computers you are deploying it may be very important to preserve user's profiles between updates. Check Redirecting Profiles for more information.