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NAS Setup: Large Drives or Smaller Drives?

ByJorge Pereira
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Here’s something that caught me off guard when building my home lab NAS: I assumed drive size was just about fitting enough terabytes in the box. Then I watched my first RAID rebuild take 36 hours on a 12TB drive, and realized I’d been thinking about this all wrong.

The question isn’t just “how much storage do I need?” It’s about rebuild times, failure risks, performance characteristics, and how you actually plan to use the thing. After going through this decision twice—once when I built my NAS, and again when I upgraded it—here’s what I wish I’d known from the start.

The Two Approaches

Large drives: Higher capacity per disk (12TB, 16TB, 20TB+)
Smaller drives: Lower capacity per disk (4TB, 6TB, 8TB)

Both work perfectly well in a NAS. The right choice depends entirely on what matters most to you.

Capacity: Fewer Drives, More Space

Large drives excel when you’re working with limited bay counts.

Four 16TB drives can deliver 48TB of raw capacity. To match that with 6TB drives, you’d need eight of them—which might not even fit in your NAS enclosure.

Large drives win here if:

  • Your NAS has 4-6 bays or fewer
  • You need to maximize storage density
  • You’re planning for capacity several years out

If bay count is your limiting factor, large drives are often your only practical option.

Cost: The Upfront vs Long-Term Trade-off

This is where the math gets interesting.

Cost per terabyte typically favors larger drives. A 16TB drive might cost $250 ($15.60/TB), while an 8TB drive runs $140 ($17.50/TB). Scale that across your array, and the savings add up.

But the upfront cost can sting. Dropping $1,000+ on four large drives all at once isn’t always feasible.

Smaller drives let you scale gradually—buy what you need now, add more later as budget and needs grow. When I first built my setup, I started with four 6TB drives and added another pair six months later. It felt more manageable than committing everything upfront.

The bottom line: If you’re designing the system all at once and have the budget, larger drives are more economical. If you prefer incremental growth, smaller drives offer more flexibility.

Reliability and Rebuild Risk: The Part Nobody Talks About Enough

This is where things get crucial, and it’s something I completely underestimated.

When a drive fails in RAID, your NAS rebuilds the missing data onto a replacement. The larger the drive, the longer this takes. My 12TB rebuild took a day and a half. An 8TB drive might finish in under 24 hours. A 4TB drive could complete overnight.

Why this matters:

During a rebuild, your array is vulnerable. If you’re running RAID 5 and a second drive fails before the rebuild completes, you lose everything. The longer that rebuild window stays open, the higher your risk.

Additionally, rebuilds stress the remaining drives. They’re reading every sector, working continuously under load. That stress can trigger failures in drives that were already marginal.

Here’s the key nuance: Modern drives have similar annual failure rates regardless of size—it’s not that large drives fail more often. But when they do fail, the consequences are more severe because recovery takes longer and involves more data.

This is why RAID 6 or RAIDZ2 (dual parity) becomes increasingly important with large drives. If you’re running 10TB+ drives, RAID 5 is genuinely risky. RAID 6 gives you that second failure buffer during rebuilds.

Smaller drives have a real advantage here in terms of faster rebuilds and shorter vulnerability windows—but proper redundancy matters more than drive size.

RAID 5 Is Increasingly Problematic for Large Drives

Worth calling out separately: RAID 5 has become questionable for modern high-capacity drives due to URE rates (Unrecoverable Read Errors).

During a rebuild, the array reads every sector on every remaining drive. With multi-terabyte drives, the probability of hitting a read error during that process is non-trivial. In RAID 5, a single URE during rebuild can cause total array failure.

My recommendation: If you’re using drives over 6-8TB, strongly consider RAID 6 or RAIDZ2 minimum. The performance penalty is minor compared to the protection gain.

Performance: More Spindles, Better Parallelism

This genuinely surprised me when I first learned it.

In many RAID configurations, more drives = better performance, especially for random I/O workloads. More physical disks mean more read/write heads working simultaneously.

A NAS with eight 6TB drives can significantly outperform one with four 12TB drives for database work, virtual machines, or anything with lots of random access patterns. For purely sequential workloads (like streaming large media files), the difference is smaller but still noticeable.

A few caveats:

  • This applies most to read performance; write performance gains depend on your RAID level
  • SSD caching can narrow the gap, though it doesn’t eliminate it entirely
  • If your workload is mostly sequential (backups, media streaming), this matters less

If you have enough bays and performance matters for your use case, smaller drives can deliver a real-world speed advantage.

Scalability and Future Planning

How you think about growth depends heavily on your hardware.

With lots of bays (8+), smaller drives let you expand incrementally. Start with four or five, add more as needed. This spreads out costs and lets you adjust to actual usage patterns instead of guessing.

With limited bays (4-6), larger drives may be your only path forward. Filling all your slots with small drives leaves you nowhere to go except replacing everything.

I found it helpful to think not just about today’s needs, but where I’d be in 2-3 years. If you’re already close to filling your bays, starting with larger drives saves you from an expensive upgrade cycle down the road.

When Large Drives Make the Most Sense

Go with larger drives if:

  • You’re maximizing capacity in a limited bay count
  • Your NAS has 4-6 drive slots or fewer
  • Your data is primarily media libraries, backups, or archives
  • You’re optimizing for cost per terabyte
  • You’re using RAID 6 or RAIDZ2 for adequate protection

This is the typical choice for home media servers and backup-focused systems.

When Smaller Drives Are the Better Fit

Choose smaller drives if:

  • Faster rebuild times and shorter vulnerability windows matter to you
  • System uptime and reliability are critical priorities
  • You need better random I/O performance
  • You have 8+ bays and prefer gradual expansion
  • You’re running workloads with lots of small file access

This approach is common in small business environments or anywhere the NAS sees heavy, constant use.

Key Lessons I’d Pass Along

RAID is not a backup. I’ll keep saying it. RAID protects against drive failure, not against accidental deletion, corruption, ransomware, or disasters. Always maintain separate backups of anything important.

Monitor your drives religiously. Set up SMART monitoring and temperature alerts. Catching a failing drive before it actually fails makes all the difference.

Plan your growth earlier than you think. I didn’t, and ended up doing a painful migration to a larger enclosure. Think about where you’ll be in three years, not just next month.

Test your rebuild process. If you’ve never actually replaced a failed drive and watched the rebuild happen, you don’t really know if your setup works. Simulate a failure in a non-critical array if possible.

What I Actually Chose (And Why)

My setup ended up being more distributed than I originally planned: three separate NAS units—two 2-bay systems and one 4-bay.

In the 4-bay system, I went with three 12TB drives (leaving one bay open for future expansion or hot spare).

Why larger drives despite all the rebuild time concerns I mentioned? Simple: bay count forced my hand. With only four bays to work with, smaller drives would have left me constantly running out of space. The math just didn’t work for my capacity needs.

I mitigated the rebuild risk by using RAID 6 (or RAIDZ2 if you’re on ZFS) for dual parity protection, and I’m religious about monitoring drive health. Yes, rebuilds take longer, but the trade-off was necessary given the hardware constraints.

The two 2-bay systems are running smaller drives in RAID 1—less capacity per unit, but they’re for different use cases where I prioritized redundancy over total storage.

Would I make the same choice again? For the 4-bay, absolutely—I didn’t have a realistic alternative. If I’d started with an 8 or 12-bay enclosure, I probably would have gone with more smaller drives. But you work with what you have, and sometimes the “optimal” choice on paper isn’t an option in practice.

Final Thoughts

There’s no universally “correct” answer here, and anyone who tells you otherwise is oversimplifying.

If capacity and cost efficiency matter most: Larger drives are hard to beat, especially in limited bay counts. Just make sure you’re using RAID 6 or better.

If reliability, rebuild times, and performance are priorities: Smaller drives often deliver better real-world results, assuming you have the bay space.

The best NAS setups aren’t built around theoretical specs—they’re designed around how you actually use your data. Think through your workload, your growth trajectory, and what would actually cause you problems if it went wrong.

For me, that clarity came after my first rebuild took a day and a half while I nervously watched the progress bar. Hopefully, you can learn from my experience and make the right call before your first drive failure.