The real cost of a NAS upgrade is not the price of the new drives — it is that price minus what your old drives are worth. This calculator computes both sides live: the cheapest in-stock drive at every larger capacity, the resale recovery of your current drives (anchored honestly to today's refurbished prices), and the net cost per added usable terabyte. In the 2026 shortage, used drives are selling at or near retail, so your upgrade is partially self-financing.
In RAID 5, capacity expands only after every drive is replaced. Swap one drive, let the array repair fully, then swap the next. Plan for 4 drives × 12-24h rebuild each — roughly a week. Partial replacement gives zero extra usable space until the last drive is in.
Single-parity arrays run degraded during every rebuild. A second drive failure mid-rebuild loses everything. Verify a full backup exists before pulling the first drive. At 16TB+, consider RAID 6.
| Target | Buy | Gross | Resale recovery | Net cost | Added usable | Net $/added TB |
|---|---|---|---|---|---|---|
| 4 × 20TBBEST | New · $310 | $1,240 | −$204-$272 | $968-$1,036 | +36TB | $26.89-28.78 |
| 4 × 24TB | Refurb · $399 | $1,596 | −$204-$272 | $1,324-$1,392 | +48TB | $27.58-29.00 |
| 4 × 22TB | New · $380 | $1,520 | −$204-$272 | $1,248-$1,316 | +42TB | $29.71-31.33 |
| 4 × 18TB | New · $309 | $1,236 | −$204-$272 | $964-$1,032 | +30TB | $32.13-34.40 |
| 4 × 16TB | Refurb · $270 | $1,080 | −$204-$272 | $808-$876 | +24TB | $33.66-36.50 |
| 4 × 14TB | Refurb · $240 | $960 | −$204-$272 | $688-$756 | +18TB | $38.22-42.00 |
| 4 × 10TB | New · $140 | $560 | −$204-$272 | $288-$356 | +6TB | $47.99-59.33 |
| 4 × 12TB | New · $230 | $920 | −$204-$272 | $648-$716 | +12TB | $54.00-59.66 |
| 4 × 32TB | New · $1,160 | $4,640 | −$204-$272 | $4,368-$4,436 | +72TB | $60.67-61.61 |
| 4 × 30TB | New · $1,200 | $4,800 | −$204-$272 | $4,528-$4,596 | +66TB | $68.61-69.64 |
Net cost = gross purchase − resale recovery of your 4 old 8TB drives. Resale is a range (60-80% of today's live refurb price, our honest ceiling). Only capacities with a live in-stock price are shown; out-of-stock sizes are excluded entirely. Sorted by net cost per added usable TB.
Used drives are currently selling at or above original retail. If you bought 8TB drives in 2022-2023, they are worth roughly what you paid — today a bare used 8TB drive is anchored to a live refurbished price of about $85, putting the honest resale range around $51-68 per drive. Your upgrade is partially self-financing: the cash you recover from the old drives directly offsets the new ones. Nobody else computes this with numbers, because it requires live prices on both sides. We have them.
Every upgrade guide on the internet tells you the price of the new drives and stops there. That is only half of the equation, and it is the misleading half. When you upgrade a NAS from smaller drives to larger ones, you end up with a stack of perfectly good drives you no longer need. Those drives have resale value, and in the current market that value is unusually high. The number that actually matters for your budget is the net cost: gross purchase price minus resale recovery.
We compute the gross side directly from live inventory. For each capacity above your current drives, the calculator finds the single cheapest in-stock drive — comparing new and refurbished — and multiplies by your drive count. Capacities with no in-stock listing are excluded entirely; you will never see a phantom "price on request" row. That keeps the ranking honest and immediately actionable: every row has a real drive behind it with a working buy link.
The resale side is where honesty matters most, because it is easy to inflate. We refuse to invent a number. The anchor for what a bare used drive is worth is the live refurbished-with-warranty price of the same capacity — that is the ceiling, since a warrantied, tested drive from a reseller is strictly more valuable than a bare drive you ship in a padded envelope. From that ceiling we take a range of 60 to 80 percent to reflect the real spread between a quick private sale and a patient one. If no refurbished anchor exists at or near a capacity, we display "insufficient market data" rather than guess. The result is always a range, never a false-precision point estimate.
Net cost is simply gross minus resale, and because resale is a range, net cost is a range too. We then divide net cost by the usable terabytes you actually gain — RAID-aware, so parity overhead is already subtracted — to produce net dollars per added usable terabyte. That single figure is the correct way to rank upgrade paths against each other, because it normalizes for both the price of the drives and the real capacity they deliver after redundancy.
Gross purchase: four new 20TB drives at $310 each = $1,240. Resale recovery: four old 8TB drives at $51-68 each = −$204-$272. Net cost: $968-$1,036 for +36TB usable (24TB → 60TB) — about $26.89-28.78 per added usable terabyte. Figures update every time prices refresh.
A NAS has a fixed number of bays. Every bay you fill with a small drive is a bay you cannot use for a bigger one later, so filling bays with more small drives is a dead end — you hit the wall sooner and with more hardware to power and cool. Replacing existing drives with larger ones does the opposite: it raises your ceiling without consuming a single additional bay, and it reduces your total drive count for the same capacity, which means fewer failure points, lower idle power draw, and less heat.
The economics reinforce the engineering. Because larger drives cost less per terabyte and because you recover cash from the drives you retire, upgrading in place usually wins decisively on net cost per usable terabyte versus buying an expansion unit or a second NAS and populating it from scratch. Adding hardware is the right call in two situations only: your bays are already full at the largest capacity you can buy, or you specifically want a physically separate second system as a backup target for a 3-2-1 strategy. In every other case, upgrade the drives you have. To sanity-check the power side of that trade, compare drive counts on the NAS devices page, and see the full three-way comparison on what to do when your NAS is full.
The mechanics matter as much as the money, because the upgrade week is the riskiest period in your array's life. Replace one drive at a time. Pull the oldest or smallest drive, insert the larger one, and let the pool repair completely before you touch anything else. In RAID 1, 5, 6, and 10 the array is degraded during each rebuild — a second failure before the rebuild finishes loses everything — so a verified backup is not optional. High-capacity drives rebuild slowly, on the order of 12 to 24 hours or more each, which is why a full four-bay upgrade realistically spans a week. Buy all your replacement drives up front so a mid-swap stock-out cannot strand you with a half-migrated array. The complete step-by-step procedure, with Synology, QNAP, and UnRAID specifics, lives on the replace NAS drives with larger ones guide.
The resale recovery in this calculator is only real if you actually sell the drives, and the channel you choose determines how much of the range you capture. For individuals, eBay is the most reliable venue: price against completed sold listings for your exact model, and single drives move quickly. Homelab communities like r/hardwareswap and dedicated forums avoid fees and reach buyers who understand enterprise pulls. Local marketplaces eliminate shipping risk entirely. ITAD firms only make sense for bulk lots, typically with a four-figure minimum — they are not interested in a handful of drives from a home NAS. Whichever route you pick, wipe every drive fully before it leaves your hands and record its SMART health so you can list it honestly. The full per-capacity value ranges and channel guidance are on the used drive value guide.
The real cost is the net cost: the price of the new drives minus what your old drives are worth on resale. For a 4-bay RAID 5 array moving from 8TB to 20TB drives at today's live prices, the gross purchase runs several hundred dollars, but selling the four old 8TB drives recovers a meaningful chunk — often 15-25% of the gross. This calculator computes gross, resale recovery (as a range), and net cost live for every capacity that is currently in stock, so you see the true out-of-pocket figure rather than just the sticker price.
Yes, and in the current shortage they are worth more than most people expect. Used enterprise and NAS drives sell readily on eBay, r/hardwareswap, and homelab forums. Because refurbished-with-warranty drives are the ceiling for a bare used drive's value, we anchor every resale estimate to today's live refurb price and show it as a 60-80% range rather than a single number. Wipe each drive fully before selling and check SMART health so you can list it honestly. See our used drive value guide for per-capacity ranges and where to sell.
In standard RAID 1, 5, 6, and 10, yes — usable capacity expands only after every drive has been replaced with the larger size and the array has repaired. Replacing just one or two drives gives you zero extra usable space in these levels; the array sizes itself to the smallest member. Synology SHR and UnRAID are the exceptions: they can deliver partial extra capacity once the largest drives are swapped, without waiting for the whole set.
Upgrading the drives in your existing NAS is almost always cheaper per usable terabyte than buying a second NAS, because you reuse the enclosure, controller, and power supply, and you recover cash by reselling the old drives. Buying more hardware wins only when your bays are already full at the top available capacity, or when you specifically want a separate backup target for a 3-2-1 strategy. Run both scenarios through the calculator and compare net cost per added TB.
Plan for a week for a full array. Each drive is replaced one at a time, and the array must fully repair before you touch the next drive. High-capacity drives rebuild slowly — roughly 12 to 24 hours or more per drive at 16TB and above, longer under heavy use. For a 4-bay array that means two to four days of rebuilding plus verification between swaps. Never rush the process by pulling a second drive before the first rebuild completes.
For a primary array that holds your only copy of important data, buy new for the full manufacturer warranty and zero accumulated wear. For a secondary tier, backup target, or any RAID 6 array with a hot spare, refurbished datacenter pulls deliver meaningfully better cost per terabyte at acceptable risk. The calculator picks whichever is cheaper at each capacity and labels the condition, so you can see exactly what you would be buying and switch if you prefer new.
The 2026 shortage inverted the used market. Western Digital is sold out of hard drives for the year at the hyperscale level, Seagate is running at partial fill, and AI datacenter demand has absorbed new production 12-18 months ahead. With new drives scarce and expensive, buyers turned to the secondary market, pushing used and refurbished prices to levels at or near original retail. That is why your installed drives have effectively appreciated and why factoring resale into an upgrade genuinely changes the math.