We have two units both working just fine after being online now 24/7 for nearly 4 months. You must set these things up right however. I experimented with them a bit first. I was able to software RAID two units together into one 30 TB volume. That was cool, but it got me a bit worried about losing data. So I reset them up as two logical drives, each using 5 drives for the RAID and allowing one to remain as a hot spare. This yields two 12 TB volumes. I lost a bit of storage potential, but it's rock solid safe now. Easy to daisy chain these together too, but there is no thunderbolt cable included. That's pretty unbelievable actually. Other than that though, a nice product.