← NAS RAID Learning Center
Step 2 · NAS RAID guide

RAID 5 vs RAID 6 for NAS

Compare RAID 5 and RAID 6 for NAS usable capacity, rebuild risk, parity overhead, drive count, and home-server buying decisions.

Use NAS calculator Open RAID selector

Guide focus

Decide whether one parity disk is enough for the planned drive count and drive size.

Single vs dual parity

1. Recalculate Confirm usable TB Run the numbers again if this guide changed your RAID level, bay count, or reserve assumption. 2. Shortlist 6-bay dual-parity plan RAID 6, RAID-Z2, media libraries, and backups 3. Protect Add backup and UPS Keep redundancy, backup, restore, and clean shutdown in the same purchase plan.

Key takeaway

RAID 5 uses one parity disk; RAID 6 uses two parity disks.

Key takeaway

RAID 6 becomes more attractive as drive size, rebuild time, and array size increase.

Key takeaway

RAID 5 can still make sense for smaller arrays with strong backups and replaceable data.

Key takeaway

Neither RAID 5 nor RAID 6 removes the need for backup.

Planning sequence

Work through the decision in order

  1. 1 Calculate usable TB for the same drive count in RAID 5 and RAID 6.
  2. 2 Estimate how long a rebuild could take for the chosen drive size and NAS workload.
  3. 3 Decide whether a second drive failure during rebuild would be acceptable.
  4. 4 Check whether the NAS platform supports online migration from RAID 5 to RAID 6.
  5. 5 Make sure the backup plan exists before choosing the higher-capacity option.

Buying checks

What to verify before checkout

  • • At least 3 drives for RAID 5 or 4 drives for RAID 6.
  • • One extra drive bay if future expansion or migration is likely.
  • • CMR NAS drives with consistent capacity and health reporting.
  • • UPS protection to reduce parity-write interruption risk.
  • • Backup target large enough for the most important data set.

Common mistakes

Avoid expensive storage regrets

  • • Choosing RAID 5 on a large array only because it shows more usable TB.
  • • Treating RAID 6 as a substitute for off-device backup.
  • • Ignoring rebuild time and workload pressure while the array is degraded.
  • • Filling the array close to 100% and leaving no room for snapshots or maintenance.

Before buying drives

Use this guide as a filter, then run the calculator again.

If the guide changes your RAID level, bay count, or drive size, recalculate usable capacity before buying. A small change in parity or reserve can move the purchase from comfortable to cramped.

Recalculate usable TB

Confirm raw capacity, usable TB, reserve, and fault tolerance.

Check backup plan

Make sure redundancy is paired with recoverable copies.

Trust layer

Audit this NAS guide before turning it into a shopping list

Every NAS guide follows the same site-wide trust pattern: explain the decision, connect it back to the calculator, name purchase boundaries, and disclose how future monetized links may work.

Step 2

This guide answers one buying decision at a time

Decide whether one parity disk is enough for the planned drive count and drive size.

Calculator loop

Capacity should be recalculated after the guide changes the plan

If this guide changes RAID level, bay count, drive size, reserve, or backup assumptions, return to the calculator before buying.

Purchase boundary

Search links are prompts, not endorsements

The buying layer uses neutral category searches until affiliate links are ready and disclosed.

Method

How to use this guide safely

Read RAID 5 is attractive because it preserves more usable capacity. RAID 6 gives up another disk of capacity to survive a second drive failure during rebuild. For modern large disks, that extra margin often matters more than the headline TB difference.
Apply Calculate usable TB for the same drive count in RAID 5 and RAID 6. Estimate how long a rebuild could take for the chosen drive size and NAS workload.
Verify At least 3 drives for RAID 5 or 4 drives for RAID 6. One extra drive bay if future expansion or migration is likely.
Recalculate Run the NAS calculator again if the guide changes capacity, parity, reserve, or bay-count decisions.

Pre-action checks

Check these before checkout

  • At least 3 drives for RAID 5 or 4 drives for RAID 6.
  • One extra drive bay if future expansion or migration is likely.
  • CMR NAS drives with consistent capacity and health reporting.
  • Prefer CMR NAS drives for RAID and ZFS pools; avoid surprise SMR drives for parity rebuild workloads.
  • Budget for at least one independent backup target because RAID protects availability, not deleted files or ransomware.
  • Check bay count, expansion path, power draw, noise, network speed, and replacement-drive availability before buying disks.

This guide is planning guidance, not vendor documentation. Product-category links are non-affiliate placeholders until monetization is ready and disclosed.

Disclosure

Editorial method

What this calculator can—and cannot—decide

The capacity model makes drive count, drive size, RAID layout, and reserve visible. It is a planning aid: it does not predict exact performance, rebuild duration, hardware compatibility, or the probability of data loss for a specific system.

Last reviewed: July 10, 2026. Product links remain neutral category searches until a partner relationship and page-level disclosure are in place.

OpenZFS checksums and scrubs Background on checksum verification, scrubs, and repair in suitably redundant ZFS pools. Read primary source ↗ TrueNAS data protection Official overview of scrubs, S.M.A.R.T. tests, snapshots, replication, and backup tasks. Read primary source ↗ CISA ransomware guidance Why recoverable, regularly tested backups should be separate from array redundancy. Read primary source ↗

Buying conversion layer

Turn this guide into a purchase-safe NAS shortlist

Use the guide as a buying filter, then compare ordinary product-category searches. These links are non-affiliate placeholders until Amazon Associates is ready.

Disclosure →

Recommended path for this guide

6-bay dual-parity plan

A more durable path for RAID 6 or RAID-Z2 buyers who want usable capacity without relying on single parity.

1. Recalculate Confirm usable TB Run the numbers again if this guide changed your RAID level, bay count, or reserve assumption. 2. Shortlist 6-bay dual-parity plan RAID 6, RAID-Z2, media libraries, and backups 3. Protect Add backup and UPS Keep redundancy, backup, restore, and clean shutdown in the same purchase plan.

Recommended pick

6-bay dual-parity plan

A more durable path for RAID 6 or RAID-Z2 buyers who want usable capacity without relying on single parity.

  • • At least 3 drives for RAID 5 or 4 drives for RAID 6.
  • • One extra drive bay if future expansion or migration is likely.
  • • Model usable capacity after two parity drives and at least 10% reserve.
  • • Prefer CMR NAS drives for parity rebuild, scrub, and resilver workloads.
6-bay NAS enclosure12TB CMR NAS driveNAS backup drive

Final checkout guardrails

  • At least 3 drives for RAID 5 or 4 drives for RAID 6.
  • One extra drive bay if future expansion or migration is likely.
  • CMR NAS drives with consistent capacity and health reporting.
  • Prefer CMR NAS drives for RAID and ZFS pools; avoid surprise SMR drives for parity rebuild workloads.
  • Budget for at least one independent backup target because RAID protects availability, not deleted files or ransomware.
  • Check bay count, expansion path, power draw, noise, network speed, and replacement-drive availability before buying disks.

Non-affiliate category search map

Open search tabs only after the guide narrows the spec.

These are ordinary product-category searches, not affiliate links. Use them to compare bay count, CMR drive class, UPS support, backup targets, warranty, noise, and return policy.

Placeholder links

FAQ

RAID 5 vs RAID 6 questions

Open NAS FAQ →
Is RAID 6 always better than RAID 5?

RAID 6 is safer for larger arrays, but it costs one more drive of capacity. RAID 5 can still fit smaller, lower-risk arrays when backups are strong.

How many drives do I need for RAID 6?

RAID 6 requires at least four drives. It becomes more capacity-efficient as drive count increases.

Should I use RAID 5 with very large drives?

Be cautious. Larger drives can mean longer rebuild windows, so many buyers compare RAID 6 or RAID-Z2 before committing.

Step 1

NAS RAID Buying Checklist

A practical NAS RAID buying checklist for choosing drive count, bay count, CMR drives, UPS protection, backup targets, and RAID level before purchasing storage hardware.

Step 3

RAID 10 vs RAID 5 for a Home Server

Compare RAID 10 and RAID 5 for home servers, including usable capacity, rebuild behavior, random I/O, drive failure tolerance, and budget tradeoffs.

Step 4

RAID-Z1 vs RAID-Z2 for TrueNAS

Compare RAID-Z1 and RAID-Z2 for TrueNAS and ZFS pools, including usable capacity, vdev planning, rebuild exposure, scrubs, checksums, and expansion tradeoffs.