It has been months since my last post. During this time the price of SD cards and SSDs has decreased drastically.
SD cards:
Samsung 256GB Evo is down from $150 in January to $110 in July, $60 in November and $45 on Black Friday
https://camelcamelcamel.com/product/B072HRDM55
SanDisk Ultra 400GB A1 is down from $250 in January to $170 in July, $115 in November and $80 on Black Friday
https://camelcamelcamel.com/product/B074RNRM2B
SSDs:
Samsung 860 EVO 500GB 2.5 Inch SATA III Internal SSD is down from $170 in January to $120 in July, $85 in November and $73 on Black Friday
https://camelcamelcamel.com/product/B0781Z7Y3S
Samsung 860 EVO 1TB 2.5 Inch SATA III Internal SSD is down from $330 in January to $220 in July, $145 in November and $127 on Black Friday
https://camelcamelcamel.com/product/B078DPCY3T
NVMe SSDs (Crucial MX500 in particular) seem to cost around $20 more than the mentioned SATA SSDs.
500GB SATA SSD costs about the same as 400GB SD card.
1TB SATA SSD now costs as much as 400GB SD card did when SG first added it as an option for SG9663DC.
All of this means that, assuming there exists a camera board with SATA III port, the two 4k camera high-quality encoding setup is no longer limited by the SD card's write speed, we can just switch to using SSD which costs about the same.
There is an upper bound to how much data you can write to SSDs before it fails. You can google "ssd endurance test" to see some findings. In practice, SSDs tend to outlive the promised TBW ratings of manufacturers, sometimes even doubling them.
Samsung 860 EVO 500GB has 300 TBW and 1TB version has 600 TBW
https://www.samsung.com/semiconductor/minisite/ssd/product/consumer/860evo/
Using
this calculator, 5 Megapixel, H.264, high quality, 2-camera, 30 FPS, 24-hour 1-day recording uses 414.7GB of storage, meaning 300 TBW would last for almost 2 years of non-stop 24-hour recording, 600 TBW would last for almost 4 years of that.
If we instead use the estimation of 50MBit/s for H.265 kamkar1 gave in an earlier post, 2-camera setup would use 1055GB of storage, meaning 300 TBW would last for almost 1 year of non-stop 24-hour recording, 600 TBW would last for almost 2 years of that. That's a bit low, but still okay-ish.
So far it sounds like using SSD is feasible in theory. The only other concern might be the power draw in comparison to the SD card, but I'm not going to go into it, too tired to continue writing this post
Anyway, looking forward to seeing dual 4k camera dashcams powered by SSDs in the near future (1-3 years?).