So, you may ask: why wouldn’t I use RAID 5 instead? It gives me 6TB of total capacity, a performance advantage, and redundancy that protects me from a single drive failure.
The biggest difference between RAID 5 and RAID 10 is how it rebuilds the disks. RAID 10 only reads the surviving mirror and stores the copy to the new drive you replaced. Your usual read and write operations are virtually unchanged from normal operations.
However, if a drive fails with RAID 5, it needs to read everything on all the remaining drives to rebuild the new, replaced disk. Compared to RAID 10 operations, which reads only the surviving mirror, this extreme load means you have a much higher chance of a second disk failure and data loss.