In Settings under the General Preferences tab, you have control over the local cache :
Local cache directory
Define the secondary location to where resource thumbnails are located when generated.
This setting is helpful to compute and store resource thumbnails when a resource path is read-only (like on a network path with only read access). This avoids recomputing thumbnails at each startup because they would not otherwise be saved on the disk.
Local cache budget (in MB)
Define the maximum size of the cache for the local store.