"OptiNAND uses a large non-volatile memory on the drive. It optimizes write performance by using DRAM as a cache. So, when the drive is powered up, performance is on par with WCE, well it is WCE technically as DRAM caching is enabled.

In the event of an emergency power off (EPO), the contents of DRAM are written to non-volatile memory (NVM) using the power of the spinning disk, so the data is protected. Since NVM can hold the data for a very long time without needing power , as soon as the drive is powered up again , the data can be transferred from NVM to the drive."

https://pnpdxb.com/blogs/hdd-2/what-is-wd-armorcache-and-opt...