FREE · NETWORK & IT INFRASTRUCTURE
RAID Calculator.
Calculate usable capacity, efficiency, fault tolerance, IOPS, throughput and rebuild time for RAID 0, 1, 5, 6, 10, 50, 60 and ZFS RAIDZ.
Hard drives under production load often rebuild at 50–150 MB/s.
- Raw capacity (including spares)
- 128 TB
- Storage efficiency
- 75 %
- Drive failures survived
- 2
- Mixed random IOPS
- 900 70 % reads, write penalty 6
- Random read IOPS
- 1,200
- Random write IOPS
- 200
- Sequential read
- 1,500 MB/s
- Sequential write
- 1,500 MB/s
- Rebuild of one drive
- 44.4 h
Other levels with 8 drives of 16 TB
| Level | Usable | Efficiency | Drive failures survived | Mixed IOPS |
|---|---|---|---|---|
| RAID 0 (stripe) | 128 TB | 100 % | 0 | 1,200 |
| RAID 1 (mirror, all drives) | 16 TB | 13 % | 7 | 885 |
| RAID 10 (striped mirrors) | 64 TB | 50 % | 1–4 | 1,020 |
| RAID 5 (single parity) | 112 TB | 88 % | 1 | 930 |
| RAID 6 (double parity) | 96 TB | 75 % | 2 | 900 |
| RAID 50 | 96 TB | 75 % | 1–2 | 930 |
| RAID 60 | 64 TB | 50 % | 2–4 | 900 |
| ZFS RAIDZ1 (one vdev) | 112 TB | 88 % | 1 | 150 |
| ZFS RAIDZ2 (one vdev) | 96 TB | 75 % | 2 | 150 |
| ZFS RAIDZ3 (one vdev) | 80 TB | 63 % | 3 | 150 |
| JBOD / span (no redundancy) | 128 TB | 100 % | 0 | 150 |
- RAID protects against drive failure, not deletion, ransomware, fire or controller faults. Keep separate backups.
- Drive makers use decimal terabytes (10¹² bytes); operating systems often show binary TiB.
How to use RAID Calculator
Choose the RAID level, number and size of drives, spares and per-drive performance. The table compares every level possible with the same drives.
How it works
Usable capacity = data drives × size. Mixed IOPS = raw IOPS × read % + raw IOPS × write % ÷ write penalty. A RAIDZ vdev delivers about one drive’s random IOPS. Rebuild time = drive size ÷ rebuild speed.
Example
8 × 16 TB drives in RAID 6 give 96 TB (87.3 TiB) usable, survive 2 drive failures and rebuild one drive in about 44 hours at 100 MB/s.
What RAID changes
RAID combines several drives into one volume to gain capacity, speed or tolerance to drive failure — never all three at no cost. The calculator shows the trade-off for the drives you have: usable space in decimal terabytes and in the binary TiB most systems display, the number of drive failures the array survives, random IOPS for your read/write mix, sequential throughput and the time to rebuild one drive.
Levels compared
| Level | Usable capacity | Survives | Write penalty | Good for |
|---|---|---|---|---|
| RAID 0 | All drives | 0 failures | 1 | Scratch space only |
| RAID 1 | One drive | All but one | 2 | Boot volumes, small servers |
| RAID 10 | Half | 1 guaranteed, up to half | 2 | Databases, virtual machines |
| RAID 5 | All but one | 1 | 4 | Read-heavy data on small drives |
| RAID 6 | All but two | 2 | 6 | Large drives, file and backup storage |
| RAID 50 / 60 | Per parity group | 1 / 2 per group | 4 / 6 | Large arrays needing more speed |
| RAIDZ1/2/3 | All but 1/2/3 | 1/2/3 | Full-stripe writes | ZFS pools |
The write penalty is the number of disk operations a small random write costs. RAID 5 must read the old data and parity and write both back: four operations. That is why the same drives deliver far fewer write IOPS in RAID 6 than in RAID 10.
The formulas
usable = data drives × drive size
mixed IOPS = raw IOPS × read% + raw IOPS × write% ÷ write penalty
rebuild time = drive size ÷ rebuild speedExample: eight 16 TB drives in RAID 6 keep six drives of data, 96 TB or 87.3 TiB. At 150 IOPS per drive and 70 % reads, the array delivers about 900 mixed IOPS. Rebuilding one drive at 100 MB/s takes about 44 hours, during which a second failure is survivable in RAID 6 but fatal in RAID 5.
ZFS RAIDZ writes full stripes, so it avoids the read-modify-write penalty, but a single RAIDZ vdev delivers roughly the random IOPS of one drive. Pools gain IOPS by adding vdevs.
Choosing a level
- Large hard drives (4 TB and up): prefer double parity (RAID 6, RAIDZ2) or mirrors. Long rebuilds make single parity risky.
- Databases and virtual machines: RAID 10 or mirrored vdevs for write IOPS.
- Archives and backups: RAID 6 or RAIDZ2 for capacity with protection.
- Always keep backups: RAID does not protect against deletion, ransomware, fire or a failed controller.
For a performance target rather than a capacity, use the storage IOPS calculator. To size the backup copy of the array, see the backup storage calculator.
Questions about RAID Calculator
Why does my 96 TB array show 87 TB?
Drive makers count 1 TB as 10¹² bytes; most operating systems divide by 2⁴⁰ and label the result TB although it is TiB. 96 TB equals 87.3 TiB.
Is RAID 5 dead?
Not for small SSD arrays, but with large hard drives the long rebuild window and unreadable sectors make a second fault likely enough that RAID 6 is the usual recommendation.
Do hot spares add capacity?
No. A spare sits idle until a drive fails, then the rebuild starts automatically. It is counted in raw capacity only.
Is RAID Calculator free, and do I need an account?
Yes. This tool is free to use in your browser without an account. Processing takes place on your device.
What are the limits and what should I check?
Assumes identical drives. ZFS padding and slop space, controller caches and filesystem overhead are not included. RAID is not a backup. Everything is calculated in your browser; nothing is sent or probed on the network. Review the result before using it in your work.
Is my input sent to a server?
Your input is processed in your browser and is not uploaded by this tool. Files and pasted text are cleared when the page is refreshed. Normal website requests are still required to load the page and its libraries. Read the privacy explanation.