Some of that can be controlled via the Preferences dialog, "file handling" tab.
The preview cache, which is a folder whose name ends with Previews.LRDATA, is by default placed on the same drive as your catalog file. You can move the catalog file and previews using your operating system to another drive; and then open the catalog file by double-clicking on it.
You can also place the Preview cache on a different drive without moving the catalog file, by using something call a symbolic link. You should be able to search the forum for instructions on how to do that.
The drawback to putting catalog and cache on a different disk is that if the disk is slower, then Lightroom's Library Module will be shower.
At the present there is no way, that I know of or have read about, to move the location of the Video Cache folder.
I was thinking there must be a Registry setting that controls this, for Windows, or a plist file on a Mac (which plist files do basically the same thing as entries in the Windows registry) but have yet to fine any entry in the Windows registry for this. So it must be hard wired into Lightroom itself and we'll have to wait for Adobe to add an option to change it.
Thanks to all who replied. I actually do have my Catalogs on a USB3 portable drive. It's only the Video cache that is annoying. I did use Preferences but other than "Purge Cache" under Video, there is no option to move it elsewhere. If anyone has any other suggestions, would be appreciated.
Can't help, but I have the same problem. To me it's a major bug. Have posted it on the Photoshop family site too.
Thanks. I did purge the C: drive based video cache and it did clear. So for now I will have to do it repeatedly.
I've written a batch file to delete the files automatically on Windows startup until this issue is fixed.
The batch file contents are below. If you are comfortable with batch files then you can probably carry on and figure out what to do, but if not, read on.
Copy the batch file contents towards the end into notepad, replacing [USER] with your Windows user name.
Go to file>save as
Browse to C:\
Save the file as
"deletevideos.bat" including the quotation marks. This will save it as a batch file.
Find the file, right click it and create a shortcut.
Right click the shortcut, select properties. Click the shortcut tab, set Run: to minimized.
Cut and paste the shortcut into C:\ProgramData\Microsoft\Windows\Start Menu\Programs\Startup
This will run the batch file when Windows starts. If you hibernate your computer or put it to sleep you might want to put that shortcut somewhere handy too.
Batch file contents....don't be tempted to replace the *.mcdb, *.pek and *.cfa with *.* !
echo Deleting LR Video Cache.............
cd C:\Users\[USER]\AppData\Local\Adobe\Lightroom\Caches\Video\Media Cache Files
del *.pek >nul 2>nul
del *.cfa >nul 2>nul
cd C:\Users\[USER]\AppData\Local\Adobe\Lightroom\Caches\Video\Media Cache
del *.mcdb >nul 2>nul