Question 1

How much usable space does RAID 5 give with 4×4TB drives?

Accepted Answer

(4 − 1) × 4 TB = 12 TB usable. One drive's worth of capacity is reserved for parity.

Question 2

What is the difference between RAID 5 and RAID 6?

Accepted Answer

RAID 5 uses single parity and survives 1 drive failure. RAID 6 uses double parity and survives 2 simultaneous failures. RAID 6 is recommended for arrays with 5 or more drives or drive capacities of 12 TB and above.

Question 3

Can I mix different drive sizes in RAID?

Accepted Answer

Traditional RAID (0, 1, 5, 6, 10) treats all drives as the smallest drive's size, wasting space on larger drives. Synology SHR and Unraid handle mixed drive sizes efficiently.

Question 4

Is RAID a backup?

Accepted Answer

No. RAID protects against drive hardware failure only. It does not protect against accidental deletion, file corruption, ransomware, fire, theft, or admin error. Always keep an independent backup, ideally off-site.

Question 5

How many drives do I need for ZFS RAIDZ2?

Accepted Answer

Minimum 4 drives. The recommended sweet spot is 6-8 drives for a good balance of capacity, performance, and fault tolerance.