You can control the LucidLink cache with the 'lucid cache' and 'lucid config' commands. 

Lucid cache can be used to see the current cache configuration and turn the cache on or off.

usage: Lucid cache [options]

display cache information as well as control the cache

    [--info]                 display cache information
    [--on]                   turn the cache on
    [--off]                  turn the cache off

Example: flush lucid cache

Lucid cache --info 
Cache enabled: true
Backend writes enabled: true
Page Size: 257KiB
Cache Size: 5GiB <-- current cache size setting

Lucid cache --off
Lucid cache --on

To change the cache size you need to use lucid config and reconnect to your filespace.

usage: Lucid config --explain [--KEY1 --KEY2 ...]

Key:               DataCache.Size
Description:       Local data cache size. Default is 5GiB. Configuration will be applied after the client reconnects to the filespace.
Value constraints: Min 100MiB. Max 1TiB. Supported unit suffixes: M(iB), G(iB), T(iB).
Default value:     5GiB

Example: change lucid cache size to 10GB (applied once there are no remaining uploads)

lucid config --set --DataCache.Size 10G
lucid deactivate
lucid activate

To change where your cache is stored on disk, please review how to link to your Filespace with a specific cache location.