It depends on how you have the cache task set up. Click the little button with the platters icon (e.g. next to the dropdown you currently have set to "MAX" in your screenshot) to see advanced options discussed below.
Options:
Read/Write cache with shared space for both
* Writes will hit the cache before being written to disk.
* Any free space in the cache will be used for writes and then persist in the cache.
* At the same time, frequently read data will be loaded into the cache from disk
* Once there's no space left in the cache, standard rules will apply - loosely, the most frequently read/written blocks will be cached
Read/write cache split into separate read and write sections
* Writes will fill the write space only
* Reads will populate the read space only, based on most frequently read blocks
Read-only cache (non-shared, with 100% space reserved for read)
* Writes will go straight to disk, bypassing the cache
* Cache will be populated from the disk based on most frequently read blocks
For your use-case I'd recommend the last option. It will make sure that your TV-tuner writes never hit the cache, and over time only your most frequently read data will fill the cache. The downside is that data you've just written to the drive won't immediately be available in the cache.
I may be slightly off on some of the specific technical behaviors of each scenario above - Jaga or a Romex employee can clarify - but I think I'm pretty close to the actual behavior
