Windows no longer does RAID, like mirroring, using Disk Management. You need to use Storage Spaces. You can create a mirror using the methods described in the article.

Storage Spaces helps protect your data from drive failures and extend storage over time as you add drives to your PC. You can use Storage Spaces to group two or more drives together in a storage pool and then use capacity from that pool to create virtual drives called storage spaces. These storage spaces typically store two copies of your data so if one of your drives fails, you still have an intact copy of your data. If you run low on capacity, just add more drives to the storage pool.

How do I create a storage space?

1. Add or connect the drives that you want to group together with Storage Spaces.
2. Go to the taskbar, type Storage Spaces in the search box, and select Storage Spaces from the list of search results.
3. Select Create a new pool and storage space.
4. Select the drives you want to add to the new storage space, and then select Create pool.
5. Give the drive a name and letter, and then choose a layout. Two-way mirror, Three-way mirror, and Parity can help protect the files in the storage space from drive failure.
6. Enter the maximum size the storage space can reach, and then select Create storage space.

Mirror spaces are designed for increased performance and protect your files from drive failure by keeping multiple copies. Two-way mirror spaces make two copies of your files and can tolerate one drive failure, while three-way mirror spaces can tolerate two drive failures. Mirror spaces are good for storing a broad range of data, from a general-purpose file share to a VHD library. When a mirror space is formatted with the Resilient File System (ReFS), Windows will automatically maintain your data integrity, which makes your files even more resilient to drive failure. Two-way mirror spaces require at least two drives, and three-way mirror spaces require at least five.