Concept of Scratch Disk - but some relative or confusing

HI All-

I am understanding that a Scratch Disk should be *large* and *fast*. Operating with that concept I installed a NvMe 1 TB Samsung thinking it would fit the bill. Obviously not, it is full, I have deleted each finished projects "Generated Optimizations and Caches" (and then SAVED those projects) - yet in Explorer, the Scratch Disk still says ~938GB full.

1) Is the Disk too small? If so how big should it be?
2) Am I doing something incorrectly when deleting Generated Optimizations and Caches?
3) Is Large and fast when used with defining Scratch Disc to be interpreted as a relative term? If relative, to what exactly?
4) When a Scratch disk runs out of space does it retain those files and then goes to the next disc in the Preferences Setting as a Temp Storage designation?

TY-

/T/

1) depends on your workflow and projects, for my use 64Tb of raided spinning disk DAS is working well when combined with another 128Tb of raided spinning disk NAS
2) i delete at the OS level, and keep folders for caches/stills inside project folders to make that easy
3) see #1 above...
4) neither, the system gags when it can't render caches due to lack of space on the target drive

1) depends on your workflow and projects, for my use 64Tb of raided spinning disk DAS is working well when combined with another 128Tb of raided spinning disk NAS
2) i delete at the OS level, and keep folders for caches/stills inside project folders to make that easy
3) see #1 above...
4) neither, the system gags when it can't render caches due to lack of space on the target drive

Dermot, your answer prompts a few questions:
1) Both RAIDS are of the RAID 10, or perhaps a RAID 6?
2) Deleting at the OS level as in doing a fresh install of the OS when jumping into a new Project?
3) Gags, as in that Scratch Disk better be darn LARGE & FAST?

I am running a 7 Disk 8TB (5400) RAID 6, with one hot failover, and Cache/Qtier 1 TB RAID 1 NvMe PCIE DAS. I was going to go 6 Disk and a RAID 10, but had too many concerns specific to redundancy and "with my luck" a 2 DISK failure on the same side. Perhaps I should get over my paranoia.

Tnx.