NAS Beginner Guide: How Many Drives Do You Actually Need?

Updated: 2026-04-29

Last updated March 2026 · 10 min read

You've decided to build or buy a NAS. Great choice. But now comes the question everyone struggles with: how many drives should you get? Too few, and you'll run out of space. Too many, and you've wasted money. This guide walks you through everything from scratch.

Try it yourself! Compare RAID configurations with your drive sizes.

Open RAID Calculator →

Step 1: What Are You Storing?

Before counting drives, figure out what goes on the NAS. Different use cases have wildly different storage needs.

Documents & Photos – A lifetime of documents, spreadsheets, and even a large photo library (50,000+ photos in RAW) fits in 1-3TB. This is the easiest use case.

Music – Even a massive FLAC music collection rarely exceeds 1-2TB. If you stream from Spotify anyway, this is negligible.

Video / Plex / Jellyfin – This is where storage gets real. A single 4K movie remux is 40-80GB. A 200-movie library in mixed quality easily fills 5-15TB. 4K-heavy collections can reach 30-60TB+.

Backups – If your NAS also backs up laptops, phones, and other devices, add 1-2TB per device. Time Machine backups for a Mac can use 500GB-1TB alone.

Surveillance – Security cameras recording 24/7 consume roughly 1-3TB per camera per month at decent quality. This adds up fast.

VMs & Docker – If you're running services, VMs need 50-200GB each. Docker containers themselves are small, but their data volumes can grow.

Step 2: Calculate Your Actual Need

Add up your use cases. Then multiply by 1.5 to 2x for growth. Storage needs only go up, and drives are cheapest when you buy them, not when you desperately need more space.

Example: 2TB photos + 10TB media + 1TB backups = 13TB needed. With 1.5x buffer: ~20TB target usable capacity.

Step 3: Factor in RAID Overhead

You don't get to use all the raw drive space. RAID uses some capacity for protection. How much depends on the RAID type.

With RAID 5 you lose one drive's worth of capacity. With RAID 6 you lose two. With Unraid you lose your largest drive. With a mirror (RAID 1) you lose half.

For our 20TB example: in RAID 5 with 4× 8TB drives (32TB raw), you get 24TB usable. That's enough with room to grow. In RAID 6 with the same drives, you'd get 16TB – cutting it close.

Step 4: Choose Your Drive Count

2 drives – Only option is RAID 1 (mirror) or Unraid with 1 data + 1 parity. You get the capacity of one drive. Good for: simple backup NAS, low-power build.

3-4 drives – The sweet spot for most home users. RAID 5, SHR-1, or Unraid give you a good balance. You get 2-3 drives worth of usable space. Good for: media server, family NAS, small homelab.

5-8 drives – Consider RAID 6, SHR-2, or Unraid dual parity. Rebuild times get long with large drives, and the risk of a second failure during rebuild increases. Good for: large media libraries, serious homelabs.

8+ drives – You know what you're doing. RAID 6, RAIDZ2/Z3, or Unraid dual parity is strongly recommended. Consider multiple RAID groups or vdevs.

Step 5: Pick Your Drive Size

The price-per-TB sweet spot shifts over time, but currently 16-18TB drives offer the best value. Don't buy the very largest available size – the premium per TB at the top end is steep.

For a budget build: fewer large drives beats many small drives. 4× 16TB is cheaper, quieter, and uses less power than 8× 8TB – and gives you the same raw capacity.

Step 6: Leave Room to Grow

Buy a NAS enclosure (or build a case) with more bays than you need right now. Starting with 4 drives in an 8-bay enclosure costs the same for the enclosure but gives you years of expansion headroom.

If you choose SHR or Unraid, you can add drives one at a time later. With traditional RAID, expansion is more complex.

Try it yourself! Compare RAID configurations with your drive sizes.

Open RAID Calculator →

Quick Reference Table

For a media-focused home NAS with RAID 5/SHR-1: 2 drives gives ~1 drive usable (very small). 3 drives gives ~2 drives usable (starter). 4 drives gives ~3 drives usable (most popular). 6 drives gives ~5 drives usable (serious). 8 drives gives ~7 drives usable (enthusiast).

Common Mistakes

Buying the cheapest drives you can find – NAS drives (WD Red, Seagate IronWolf, Toshiba N300) are designed for 24/7 operation. Desktop drives in a NAS are a gamble.

No backup – RAID is not a backup. Your NAS protects against drive failure, not against ransomware, deletion, or fire. Budget for at least one external backup drive.

Maxing out on day one – Start with fewer drives and expand later. You'll have a much better understanding of your actual needs after 6 months of use.