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6 × 8 TB in RAID 6

Usable space, rebuild time and read error risk for 6 drives of 8 TB each.

6 × 8 TB drives in RAID 6 give 32 TB of usable space, which Windows shows as 29.1 TB. 16 TB goes to parity, so 67% of the 48 TB raw space is usable. The array survives any two failed drives, and it is still protected while one drive rebuilds.
TB

Size printed on the drive label. Different sizes? The array uses the smallest one for every drive.

Advanced settings
MB/s

Typical hard drive: 100–200 MB/s with no other load. SSD: 400 MB/s or more.

From the drive datasheet. It is a worst-case spec, so real drives usually do better.

Show capacity in
32TB usable

Array healthy
Your data Parity or mirror copy Failed drive Click a drive to make it fail.
Drawing6 × 8 TB in RAID 6
Raw48 TB
Efficiency67%

Drives that can fail

Rebuild of one drive

Read error during rebuild

Checks for this setup

The same drives in every RAID level

6 drives of 8 TB each.

LevelUsableEfficiencyDrives that can failRebuildRead error in rebuild
48 TB
100%
None
—
—
8 TB
17%
Any 5
14 h
Fixed by another copy
40 TB
83%
Any 1
14 h
27%
32 TB
67%
Any 2
14 h
Fixed by parity
24 TB
50%
1 to 3
14 h
6.2%
32 TB
67%
1 to 2
14 h
12%
Needs at least 8 drives

6 × 8 TB in RAID 6: the numbers

Usable space32 TB (29.1 TB in Windows)
Raw space48 TB
Used for protection16 TB
Efficiency67%
Drives that can failAny 2
Rebuild at 150 MB/s14 h
Rebuild at 50 MB/s (busy)44 h
Data read during rebuild40 TB
Read error risk, desktop drives96% (corrected)
Read error risk, NAS drives27% (corrected)

Rebuild

Replacing a failed drive means writing a full 8 TB drive. At 150 MB/s with no other load that takes about 14 h; on a busy array running at 50 MB/s, about 44 h. The rebuild reads every surviving drive: 40 TB in total.

Read errors

Reading 40 TB, the chance of at least one unreadable sector is 96% with desktop drives (1 per 1014 bits) and 27% with NAS drives (1 per 1015). The second parity corrects it, so the rebuild finishes without losing data.

Our take

For 8 TB drives this is the setup most administrators would choose: the rebuild takes 14 h, and the array stays protected the whole time.

Similar setups

7 × 8 TB in RAID 6More drives: 40 TB usable5 × 8 TB in RAID 6Fewer drives: 24 TB usable6 × 10 TB in RAID 6Bigger drives: 40 TB usable6 × 6 TB in RAID 6Smaller drives: 24 TB usable6 × 8 TB in RAID 5Same drives: 40 TB usable6 × 8 TB in RAID 10Same drives: 24 TB usable

All RAID 6 setups

Usable space in TB. Pick a cell for the full numbers.
Drives2 TB4 TB6 TB8 TB10 TB12 TB14 TB16 TB18 TB20 TB22 TB24 TB
4 drives4812162024283236404448
5 drives61218243036424854606672
6 drives81624324048566472808896
7 drives102030405060708090100110120
8 drives1224364860728496108120132144
10 drives163248648096112128144160176192
12 drives20406080100120140160180200220240