Can I add bigger drives later?

Yes, on Unraid, Synology SHR, and TrueNAS (with OpenZFS 2.3 RAID-Z expansion). On TrueNAS mirror vdevs, you can replace both drives with larger ones one at a time. Plan for this from day one — don't max out the bays now if you might want to grow.

Should I get one big NAS or two smaller ones?

For most homes, one bigger NAS is simpler. Two smaller ones make sense only if you want one as a backup destination for the other (which is a real 3-2-1 strategy if the second NAS is offsite at a relative's house).

Is SSD storage worth it on a NAS?

For bulk storage in 2026, no — HDDs are $24-30/TB, NAS-grade SSDs are $80-150/TB. For a cache layer (small SSD speeds up frequent reads/writes against a big HDD pool) or running VMs and Docker containers, yes. Most homes don't need it.

Backups & Storage · Beginner explainer

How much NAS storage do I need?

The honest answer to "how much NAS storage do I need" is roughly double whatever you'd guess after looking at your current files. Storage is the one home-tech buying decision where running out is painful (data migration is a week of work) and overshooting is cheap (an unused bay sits there quietly). This page walks the math, the RAID overhead reality, and why "I'll just add a drive later" is harder than the marketing suggests.

The mental model

Buying NAS storage is like planning a kitchen pantry for a household that's growing. You don't size the pantry for what's on the shelves today — you size it for the holidays, the next kid, the Costco run, and the food you'd buy if you had the room. You also leave one empty shelf, because the moment you have a fully packed pantry you start throwing food away.

**Double what you think** — size for the holiday, not today.
**Leave a bay empty** if budget allows — the pantry shelf, the cheapest insurance you can buy.
**RAID does not merge drives into one big pool the way intuition expects** — each drive holds what it holds; parity eats the difference.

Words you will see

Usable capacity: The actual storage you can use after RAID takes its cut for redundancy. A 4-bay NAS with four 16 TB drives is 64 TB raw, but only 48 TB usable with one-drive protection (RAID-5/SHR-1) and 32 TB usable with two-drive protection (RAID-6/SHR-2).
Parity: The "spare math" the NAS computes across all drives so it can reconstruct one (or two) failed drives. Parity costs one drive's worth of space per drive of protection.
SHR-1 / SHR-2: Synology's parity scheme. SHR-1 = survives one drive dying. SHR-2 = survives two. SHR's superpower: it works with mixed drive sizes and uses most of the bigger drives' extra space. Traditional RAID and ZFS can't do that.
RAID-Z1 / RAID-Z2: ZFS's version of single- and double-parity. Used by TrueNAS and Unraid/Synology ZFS pools. Same idea as SHR but with stricter rules — all drives in one vdev should be the same size, or you waste the difference.
Pool / vdev: The set of drives that work together as one storage group. A pool can have multiple vdevs. Most home NAS setups are one pool, one vdev. Growing means either replacing drives one by one with larger ones, or adding a whole new group.
Hot-swap bay: A drive slot you can pull a drive out of and slide a new one into while the NAS is running. Most home NAS units (Synology, QNAP, UGREEN, Asustor) are hot-swap; barebones builds aren't.
Headroom: Empty space you deliberately leave on the NAS. Both for performance (ZFS slows down past ~80% full; Synology recommends staying under 85%) and for expansion. Plan to keep at least 20% free.

Start with the math, not the marketing

List everything in three buckets:

**Irreplaceable now**: photo library, home videos, tax/legal docs, scanned letters. For most families this is 200 GB to 2 TB combined.

**Replaceable but inconvenient**: ripped Blu-ray/4K library, downloaded games, music collection. Often 1-10 TB depending on resolution.

**Backup of devices**: all laptop and desktop backups. Roughly the sum of all device storage × 1.5 (backups keep historical versions). A family with two 1 TB MacBooks and two 512 GB Windows laptops = ~4.5 TB.

Add them. Multiply by 2.0 for "double what you think." That's your 5-year target usable capacity. For a typical family that's 8-20 TB usable; with a heavy 4K Plex library, 30-50 TB usable.

Photos, videos, and the iPhone 17 ProRAW reality

The 2026 photo math has shifted. Modern iPhone HEIC photos: 6-10 MB each (vs 3-5 MB on iPhone 12). ProRAW: 40-50 MB per photo. ProRes 4K 30fps video: ~6-7 GB per minute. ProRes 4K 60fps: ~7 GB per minute. ProRes 4K 120fps: ~14 GB per minute.

A heavy household photo user generates roughly 10 GB per person per month, or 100-150 GB per person per year. A family of four with two of those users and two casual users lands at 300-400 GB/year of photo growth alone. Five years out, that family is 1.5-2 TB into the photo bucket.

Plex / Jellyfin library sizing if you go that route

**1080p compressed** (x265 web rips): 2-6 GB per movie. 500 movies: 1.5-3 TB.

**1080p remux** (untouched Blu-ray): 20-50 GB per movie. 500 movies: 10-25 TB.

**4K remux** (untouched UHD Blu-ray, HEVC HDR): 60-90 GB per movie typical. 500 movies: 30-45 TB.

TV shows: roughly 1-3 GB per 1080p episode, 4-15 GB per 4K episode.

Honest beginner advice: **start with 1080p compressed.** You won't see the quality difference on a 65" TV from 8 feet away, and the storage savings are 10-20x. If you genuinely care about 4K HDR, plan a separate drive for the 4K library.

RAID overhead — the line item beginners always miss

Math that actually matters:

**4-bay with 16 TB drives**: 64 TB raw → 48 TB usable RAID-5/SHR-1, 32 TB usable RAID-6/SHR-2.

**4-bay with 20 TB drives**: 80 TB raw → 60 TB SHR-1, 40 TB SHR-2.

**6-bay with 16 TB**: 96 TB raw → 80 TB SHR-1, 64 TB SHR-2.

**8-bay with 16 TB**: 128 TB raw → 112 TB SHR-1, 96 TB SHR-2.

Multiply usable by 0.80-0.85 for realistic headroom (file system overhead, free-space buffer). A 4-bay with four 16 TB SHR-1: 48 TB usable × 0.85 = ~41 TB actually comfortable.

With 4+ drives, prefer two-parity (SHR-2 / RAID-Z2) — the probability of a second drive failing during the rebuild of the first one is real and growing with modern drive sizes.

Drive size sweet spot in 2026 + the hot-swap rule

The 2026 sweet spot is **16-20 TB drives**, not 24+ TB. Three reasons:

**Rebuild time** — a failed 24 TB drive takes 24-48 hours to rebuild; 16 TB is 12-24 hours. During rebuild, the array is vulnerable to a second failure.

**Failure consequence** — losing a 16 TB drive's worth of data is bad; losing a 26 TB drive's worth is worse.

**$/TB in 2026** — 16-20 TB at $24-30/TB; 24 TB at $20-26/TB. The 24 TB tier is cheaper per TB, but the rebuild penalty is real.

**Hot-swap headroom rule**: if budget allows, buy one more bay than you need and leave it empty. That empty bay means when a drive fails or you want to expand, you slide a new drive in *without* pulling a working one.

"I'll add a drive later" is platform-specific

**Unraid 7.x (7.3.1 stable, May 2026)**: drop in one drive of any size, run parity sync, done. Best-in-class for incremental expansion.

**Synology DSM 7.3 SHR**: add one drive at a time, or replace existing drives with larger ones. DSM 7.3 restored third-party drive support after the 2025 lock-in mess.

**TrueNAS Scale 25.10 Goldeye (OpenZFS 2.3)**: RAID-Z expansion finally works as of January 2025 — you can add one drive to an existing RAID-Z vdev. Catch: existing data stays at the old parity ratio; only new writes use the wider stripe.

**TrueNAS Scale, mirrored pools**: still can't add a single drive — add a mirror pair (2 drives) or upgrade both existing drives to larger ones.

If "I'll add drives later" is your plan, Unraid or Synology SHR is the easier life.

Common misconceptions

Many people think: 8 TB is plenty for a family.

Actually: A family of four with current iPhones generates 40-100 GB per person per year of irreplaceable media. Add laptop backups (200-500 GB each) and a Plex library, and 8 TB is a 2-3 year horizon, not 10 years. The realistic 2026 family starting point is 16-32 TB usable, in a 4-bay box.

Many people think: RAID makes my four 16 TB drives into one big 64 TB drive.

Actually: RAID doesn't merge drives that way. A 4-bay with four 16 TB drives in RAID-5/SHR-1 gives 48 TB usable. In RAID-6/SHR-2 you get 32 TB. And RAID-Z1 caps every drive in the vdev at the smallest drive's size — SHR is the exception that handles mixed sizes gracefully.

Many people think: I'll fill a 20 TB drive eventually.

Actually: Most home users never fill a single 20 TB drive — and the goal isn't to fill it, it's to avoid filling it. ZFS performance degrades past ~80% full. Practical usable space on a 20 TB drive is closer to 16 TB.

Many people think: I'll just add a drive later when I run out.

Actually: Depends entirely on the platform. Unraid: easy. Synology SHR: easy. TrueNAS / ZFS: now possible with OpenZFS 2.3's RAID-Z expansion, but with caveats. Mirror vdevs: still can't add one drive. Plan upfront accordingly.

Many people think: Maxing out the bays now is cheaper than upgrading later.

Actually: It is more expensive and riskier. Drive prices fall over time, so the drive you buy in two years is at worst the same price as today's. Filling all bays now also leaves zero room for hot-swap recovery.

Ready to actually fix it?

Once you have a target capacity, the rest of the planning has tools and guides ready:

Last reviewed

2026-05-27