Review on High Performance Thunderbolt 4TB My Book RAID External Hard Drive - WDBUTV0040JSL-NESN by Adam Stone

I just connected this drive to my Mac Pro and it works as advertised. It's also quiet and accessing the spare drive is pretty easy. However, I was surprised to find that Apple's software RAID is used for mirroring instead of directly implementing hardware RAID. Why should you care? Because in my experience Apple's software RAID is not very good. Specifically, when it detects a read error on a disk, it considers the entire disk as bad. Let's assume that Disk #2 actually fails. You pull it out and replace it with a new disk #2. At this point, the software RAID will replicate the contents of disk #1 to disk #2. However, when it encounters a read error while reading from disk #1 , it will refuse to restore the RAID with full functionality and you will have to restore from a backup. It may seem unlikely, but Western Digital's data sheet for drives in this device lists a maximum uncorrectable read error rate of 1 in 10^14 bits. Consider that a 4TB hard drive contains 4 * 10^12 * 8 = 0.32 * 10^14 bits. So if you read the entire disk, there is up to a 32% chance of an uncorrectable read error. doh This actually bit me on the RAID I'm using to replace this drive. The sad conclusion is that using RAID 1 (mirroring) on this drive results in much less reliability than you would expect and is no substitute for frequent backups. Disc Specifications: http://www.wdc.com/wdproducts/library/SpecSheet/ENG/2879-771442.pdf