RAID 5 with four 4 TB drives: capacity, parity penalty, and rebuild-risk reality
RAID 5 with four 4 TB drives uses single distributed parity, giving you 12 TB of usable capacity (3 drives' worth) from 16 TB raw. It can survive any single drive failure without data loss, and read performance scales with the number of data drives. This has been the default RAID level for small-to-medium NAS units for over a decade.
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Survives 1 drive failure
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The parity calculation imposes a write penalty: every write requires reading the existing data and parity, computing new parity, and writing both. This makes RAID 5 significantly slower on random writes than RAID 0 or RAID 10. The bigger concern in 2026 is rebuild time. A 4 TB drive takes 8-24 hours to rebuild depending on controller speed and array activity. During that entire window, a second drive failure (more common than you'd think, especially with drives from the same batch) destroys the array. With 4 TB and larger drives, many storage professionals now recommend RAID 6 (double parity) for arrays of 4+ drives.
Verdict
RAID 5 with 4×4 TB is a reasonable home NAS config that balances capacity, speed, and safety. But be aware of the rebuild-risk window. If your data is irreplaceable, step up to RAID 6 or supplement with a separate backup. The days of RAID 5 being worry-free ended when drive capacities crossed 2 TB.
Frequently asked questions
How long does a RAID 5 rebuild take with 4 TB drives?
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