RAID 1 ----- Can I mix HD's with slighly different specs?

1. Western Digital 8TB WD Blue PC Hard Drive HDD - 5640 RPM, SATA 6 Gb/s, 128 MB Cache
2. Seagate BarraCuda 8TB Internal Hard Drive HDD – 3.5 Inch Sata 6 Gb/s 5400 RPM 256MB Cache

 

IIRC, RAID 1 is simply a hard drive clone. As long as capacity is the same, performance specs and form factor should not matter in that case.

 

Be sure to use a journaling file system.

 

This will be just fine. Disk size can be different but the array will have the capacity of the smallest drive.