## RAID (Redundant Array of Independent Disks) Levels 1. **RAID 5**: This is a popular choice for a four-bay NAS. It offers a good balance by providing redundancy (one disk failure tolerance) while maximizing storage capacity. With 4x18TB drives in RAID 5, you’d get approximately 54TB of usable storage. It also provides decent read speeds due to striping but is a bit slower on writes compared to RAID 10. 1. Usable storage = `(n-1) x s` 1. n=number of drives 2. s=storage in TB 2. If a second drive fails during resilvering, all data is lost. 2. **RAID 6**: RAID 6 is similar to RAID 5 but with an extra layer of redundancy, allowing up to **two disk failures**. It’s ideal for environments where data integrity is paramount. While the write performance can be slower than RAID 5, RAID 6 provides an added safety net, making it preferable for critical data storage. 1. Usable storage = `(n-2) x s` 1. n=number of drives 2. s=storage in TB 3. **RAID 10**: If performance is a top priority, RAID 10 provides better write speeds than RAID 5 or 6, especially for tasks with high I/O. It mirrors and stripes data but limits usable storage due to mirroring. It’s ideal if you run applications requiring high-speed access, but you’ll sacrifice some storage space for performance. 1. Usable Storage = `(n/2) x s` 1. for *even* n ONLY 2. n=number of drives 3. s=storage in TB https://www.servethehome.com/raid-calculator/raid-reliability-calculator-simple-mttdl-model/ https://jro.io/r2c2/