FYI: And next to my in-memory DB I use the Rock PI’s eMMC memory with an SD card adapter. If the system is critical, I prefer not to get random SD card failures, even if this is more expensive then an SD card. There are lot of log files, entity states, etc. also written to the SD card. 
I’ve bought these:
- eMMC: https://www.aliexpress.com/item/4000419649482.html (another: https://www.aliexpress.com/item/10000316343983.html)
- SD adapter: https://www.aliexpress.com/item/1005001860123203.html (this is unavailable now, so another: https://www.aliexpress.com/item/1005005502156695.html and https://www.aliexpress.com/item/10000316342734.html)
- USB adapter: https://www.aliexpress.com/item/4000598832565.html (this is unavailable now)