The temporary files underneath the \App_Data\mediaIndexing folder might not be removed automatically. These files might consume all available disk space.
As a quick temporary solution, delete all files in the mediaIndexing folder.
To resolve the issue, consider one of the following options:
<sitecore>
<scheduling>
<agent type="Sitecore.Tasks.CleanupAgent">
<files hint="raw:AddCommand">
<remove folder="/App_Data/mediaIndexing" pattern="*.*" maxAge="00.01:00:00"/>
</files>
</agent>
</scheduling>
</sitecore>