RAID Calculator
Calculate storage capacity, performance, and fault tolerance for different RAID configurations. Perfect for planning your storage setup.
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RAID Level Information
RAID 0 (Striping)
Data is striped across all drives for maximum performance but offers no redundancy. One drive failure results in total data loss.
RAID 1 (Mirroring)
Data is mirrored between drives, providing excellent redundancy but at 50% capacity efficiency.
RAID 5 (Striping with Parity)
Data and parity information are striped across drives. Can survive one drive failure with good read performance.
RAID 6 (Striping with Double Parity)
Similar to RAID 5 but with two parity blocks, allowing for two drive failures. Better for larger arrays.
The Ultimate RAID Calculator (2025): Free Tool + Complete Guide to Choose the Right RAID Level
Are you planning to build storage? Is your first question: which RAID level should you choose? Our free RAID calculator will answer all these questions, where you can calculate everything to your advantage and build the perfect storage.
2025 is here, and if you’re building a high-performance NAS, home server, or enterprise storage array, the first and most important question is: which RAID level is right for you?Choosing the wrong RAID configuration could cost you dearly in the form of wasted storage capacity, slow performance, or, in the worst case, complete data loss.
That’s why we’ve created the world’s best free RAID calculator, an absolutely accurate and mobile-friendly tool that will instantly tell you usable capacity, fault tolerance, read/write performance, and rebuild risk for RAID 0, 1, 5, 6, 10, 50, and 60.
This article gives you that calculator, along with a complete and updated 2025 guide, so you can easily make the smartest decision for yourself.
What Is RAID and Why Does It Still Matter in 2025?
RAID, which stands for ‘Redundant Array of Independent Disks’, combines multiple hard drives or SSDs into a single logical unit. Its advantage is that both performance and capacity are increased, and data remains secure. Even with the advent of ZFS, Ceph, and cloud storage, many people still prefer to use old hardware and software RAID.
- Synology, QNAP, and TrueNAS home servers
- Small business file servers
- Video editing workstations
- Game servers and Plex media servers
- Enterprise SAN/NAS systems
RAID Levels Explained with Real-World Examples (2025 Updated)
RAID 0 – Maximum Speed, Zero Redundancy
Best for: Video editing scratch disks, gaming VMs, temporary caches
Formula: Usable Capacity = Total Raw Capacity
Example: 8 × 10 TB drives = 80 TB usable
Pros: Fastest possible read/write (8× single drive speed)
Cons: One drive failure = total data loss
2025 reality check: Still popular for 8K video editing where data is backed up elsewhere.
RAID 1 – Simple Mirroring
Best for: Operating system drives, critical databases
Formula: Usable Capacity = Capacity of Single Drive
Example: 4 × 8 TB drives = only 8 TB usable (but 3-drive failure tolerance)
Pros: Excellent read performance, simple rebuild
Cons: Only 50% storage efficiency with 2 drives
RAID 5 – The Classic Balance (Still Relevant)
Best for: General-purpose file servers, small business NAS
Formula: Usable Capacity = (N – 1) × Single Drive Capacity
Example: 6 × 16 TB drives = 80 TB usable, can survive 1 drive failure
Efficiency: 83.3% with 6 drives
Warning in 2025: With 20+ TB drives, rebuild times can exceed 48 hours — increasing risk of second failure (URE problem).
RAID 6 – The Safe Choice for Large Drives
Best for: Anyone using 16 TB+ drives (recommended in 2025)
Formula: Usable Capacity = (N – 2) × Single Drive Capacity
Example: 10 × 18 TB drives = 144 TB usable, survives 2 simultaneous failures
Why it’s winning in 2025: Modern drives are so large that RAID 5 is considered risky by most experts.
RAID 10 – Performance + Safety (The Gold Standard)
Best for: Databases, virtualization hosts, high-IOPS workloads
Formula: Usable Capacity = Total Capacity × ½ (requires even number of drives)
Example: 8 × 12 TB drives = 48 TB usable, can lose up to 4 drives (if not mirrored pairs)
Pros: Excellent random I/O, fast rebuilds
Cons: Only 50% efficiency
RAID 50 & 60 – Enterprise Large-Scale Arrays
Used in 24+ bay systems where you want both performance and double/triple failure protection.
RAID Capacity & Performance Formulas (2025)
| RAID Level | Usable Capacity Formula | Minimum Drives | Max Drive Failures Tolerated | Relative Read Speed | Relative Write Speed | Storage Efficiency |
|---|---|---|---|---|---|---|
| RAID 0 | N × Drive Size | 2 | 0 | N× | N× | 100% |
| RAID 1 | 1 × Drive Size | 2 | N–1 | ~N× | ~1× | 50% (2 drives) |
| RAID 5 | (N–1) × Drive Size | 3 | 1 | ~N× | ~(N×0.75) | 67–94% |
| RAID 6 | (N–2) × Drive Size | 4 | 2 | ~N× | ~(N×0.5) | 50–92% |
| RAID 10 | (N/2) × Drive Size | 4 (even) | Up to N/2 | ~(N/2)× | ~(N/2)× | 50% |
| RAID 50 | N × Drive Size × 5/6 | 6 | 1 per RAID 5 set | High | Medium-High | ~83% |
| RAID 60 | N × Drive Size × 6/8 | 8 | 2 per RAID 6 set | High | Medium | ~75% |
Real-Life Example: Building a 100 TB Usable NAS in 2025
Goal: ~100 TB usable, survive at least 2 drive failures, good performance.
Option 1 – RAID 6 (Most Popular Choice)
- Drive size: 18 TB each
- Number needed: 9 drives
- Calculation: (9 – 2) × 18 TB = 126 TB usable
- Cost-efficient, widely supported (Synology, TrueNAS, UnRAID, mdadm)
Option 2 – RAID 10 (Faster, More Expensive)
- Drive size: 20 TB each
- Number needed: 12 drives
- Calculation: (12 / 2) × 20 TB = 120 TB usable
- Faster random I/O, faster rebuilds
Our Raid calculator instantly compares both setups side-by-side.
Why Most RAID 5 Arrays Fail in 2025 (And What to Use Instead)
With 16–24 TB drives now common, the probability of an Unrecoverable Read Error (URE) during a RAID 5 rebuild is unacceptably high. Industry rule of thumb:
- 12 TB and smaller → RAID 5 usually safe
- 14 TB and larger → Use RAID 6 or RAID 10 instead
This is why Synology now defaults new volumes to SHR-2 (their version of RAID 6).
Final Recommendation for 2025
| Use Case | Recommended RAID Level | Reason |
|---|---|---|
| Home photos & documents | RAID 6 or SHR-2 | Survives 2 failures, large drives |
| 4K/8K video editing workstation | RAID 0 + backup | Speed is critical |
| Plex/media server | RAID 6 | Large drives, long-term reliability |
| Small business file server | RAID 6 or RAID 10 | Balance of cost and performance |
| Virtualization/VM host | RAID 10 | Best random I/O performance |
| Maximum data protection | RAID 60 or multiple RAID 6 vdevs | Enterprise-grade safety |
Ready to create your best RAID setup? Use this free RAID calculator. Select your RAID type, drive size, and number of drives, and you’ll get the result instantly! No sign-up, no backlinks, and if you save the page, it’ll even run offline without any problems.
Frequently Asked Questions
Is RAID a backup?
RAID’s job is to protect data in the event of a hard drive failure. However, if you accidentally delete a file, suffer a ransomware attack, a fire, or your system is hacked, RAID can’t help. Therefore, backup is essential, following the 3-2-1 rule.
Should I use hardware RAID or software RAID in 2025?
Software RAID (such as ZFS, btrfs, mdadm) is generally considered superior because even if the controller fails, the data remains completely safe. It also offers stronger data integrity features.
Can I mix different size drives?
Some specialized software RAIDs (such as Synology SHR, UnRAID, etc.) allow you to mix different sized drives, allowing you to use the extra space efficiently. The “smallest drive fits all” rule doesn’t apply here.
What’s better: RAID 5 or RAID 6 in 2025?
RAID 6 is strongly recommended for any drive 14 TB or larger.
How long does a rebuild take with 20 TB drives?
24–72 hours depending on workload. During this time, your array is vulnerable.
Is RAID 0 safe if I have cloud backup?
Yes, absolutely. Many professionals use RAID 0 to get maximum speed, but they also take regular cloud/offsite backups.
Save this page as a bookmark — it’s the only RAID calculator you’ll ever need in 2025 and beyond.
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