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RAID for home NAS builders: RAID 5 vs RAID 6 vs RAID 10 explained

Last updated 2026-06-24

Use RAID 5 for a 4-drive home NAS with 4 TB or smaller drives. Switch to RAID 6 for 6+ drives or 8 TB+ drives. Pick RAID 10 only if VMs or databases need fast random writes.

Usable Capacity

12 TB

Total Capacity

16 TB

Storage Efficiency

75%

Fault Tolerance:

Survives 1 drive failure

RAID 5 on 4 × 4 TB drives, pre-loaded. Flip the level to 6 or 10, or bump the drive size up to 8 TB.

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Home NAS builders face a real trade-off between capacity, safety, and performance. RAID 5 with four drives gives you 75% of raw capacity and tolerates one failure. RAID 6 with six drives gives 67% and tolerates two. RAID 10 with four drives gives 50% and avoids the parity penalty on writes.

Why this matters for you

The deciding factor is rebuild time. With 4 TB drives, a RAID 5 rebuild takes roughly 7 hours on a quiet array and stresses every remaining drive. With 8 TB drives it's roughly 14 hours. Larger drives or a busy array can push a rebuild to a day or more. The longer the rebuild, the higher the chance of a second failure during it. That's why RAID 6 is the safer pick for arrays with 6+ drives or any drive larger than 6 TB. RAID 10 avoids the parity penalty entirely but costs you 50% of raw capacity, which hurts on a home budget.

Usable space before you buy drives

RAID 5 gives you the space of every drive but one. RAID 6 gives every drive but two, and RAID 10 gives half. Four 8 TB drives in RAID 5 hold 24 TB, six 8 TB drives in RAID 6 hold 32 TB, and four 8 TB drives in RAID 10 hold 16 TB.

Your NAS will show less than that. Drive makers count 1 TB as 10¹² bytes, while most operating systems count in binary units, so 24 TB shows up as about 21.8 TiB. The file system and snapshots take a little more on top.

Why big drives push you toward RAID 6

Drive spec sheets list an unrecoverable read error rate, often 1 in 10¹⁴ bits for desktop drives and 1 in 10¹⁵ for many NAS and enterprise models. 10¹⁴ bits is 12.5 TB. Rebuilding a 4-drive RAID 5 array of 8 TB disks means reading all three survivors, 24 TB in total, with no redundancy left if a sector can't be read.

That spec is a worst case, not a measured failure rate, and plenty of rebuilds finish fine. RAID 6 still holds a second layer of parity during that window, which is why it suits large drives and wide arrays.

RAID isn't a backup

RAID keeps the NAS online when a disk dies. It doesn't protect you from deleted files, ransomware, a failed controller, or a house fire, because every change is written to all drives at once. Keep at least one copy of important data on another device, and ideally one offsite.

Verdict

RAID 5 suits four drives up to 4 TB, and RAID 6 is the safer step up for 6+ drives or 8 TB+ drives because rebuilds take longer as drives grow. RAID 10 is worth its 50% capacity cost only for VM or database writes. Keep a separate backup with any of them.

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Frequently asked questions

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

12 TB, or about 10.9 TiB as most operating systems show it. One drive's worth of space holds parity, so you can lose any single drive without losing data.

Can I add a drive to a RAID 5 array later?

Often, though not on every system. Linux mdadm can reshape an array to add a disk, and OpenZFS added RAIDZ expansion in version 2.3. A reshape reads and rewrites the whole array, so it can take many hours on large drives. Make a backup first.

Is RAID 1 a good choice for a 2-bay NAS?

Yes. RAID 1 mirrors the two drives, so you get the space of one and can lose either. It's the simplest redundant layout, and a rebuild only has to copy one disk.