Here is a brief review of the 8TB My Cloud Mirror drive. The drive was set up as a JBOD. The second drive was configured as a backup of the first drive. It has the latest firmware version. I was using Windows 7 on my PC.
Wireless Transfer - Extremely slow. Using 802.11n, 5GHz channel, the transfer rate was between 4.5MB/s to 5.8MB/s.
Wired Transfer - Much faster. Using Gigabit Ethernet, the transfer rate was between 25 to 38MB/s.
File Management Via Windows Explorer - I tried to move files around using the cut and paste method. The drive does not perform the task reliably. Not all the files would move in a single task. Initially it looked like the move was complete but later find some files left behind in the old folder. A second cut and paste needed to be done.
File Format - Not Windows compatible. You cannot stick the drive into into a Windows PC and expect to access the files. This means if the electronics fail, you cannot access the files by using a PC. You need to use another NAS.
Risk of Total Data Loss - There is scenario where you could loose all your data. Say your My Cloud Mirror electronics fail (not the drive), and you buy another My Cloud Mirror drive body, and stick in your hard drive, you need to change to JBOD because the NAS is originally configured as a RAID 1. What happens then is that the NAS automatically reformats your drive. Well, you are screwed. All your data are gone.
In conclusion, I find that this product is not ready for prime time. Wireless transfer is extremely slow, there are bugs in the file management and the risk of total data loss is possible due to automatic reformatting of the drive.