My neighbor called me last spring in a small panic. His four-bay Synology had been humming away for three years, he had a backup routine he was proud of, and then a burst pipe took out the shelf it lived on. Both copies gone, because both copies were in the same closet.
That is the whole reason offsite backup exists. And the question everyone asks right after they understand that is a money question: what does keeping a copy somewhere else actually cost per month?
I have run all three of the common approaches for years, on my own gear and for people I help. Below is the real math, not the marketing math.
The three offsite options and how they charge you
There are really only three ways home users get a copy of their NAS out of the building. Cloud storage that bills per terabyte. A second NAS at a friend's or relative's house. And a rotating pair of external drives you physically carry offsite.
Each one hides its cost in a different place. Cloud is a predictable monthly line item. A second NAS is a big one-time spend with tiny running costs. Rotating drives are cheap up front but expensive in your own time and discipline.
Let me put dollars on each, using capacity tiers most homes actually sit in.
Cloud backup: the predictable monthly bill
Cloud is the option most people land on first, and for good reason. There is no hardware to buy, no second house to borrow, and the copy is genuinely far away.
The trap is that not all cloud storage is priced the same, and the cheap-looking ones often charge you again to get your data back.
Backup services versus raw object storage
A service like Backblaze personal backup is a flat fee per computer, but it backs up a PC, not a NAS directly, so most NAS owners skip it. What NAS owners actually use is object storage: Backblaze B2, Wasabi, or one of the big three clouds, paired with a tool like Hyper Backup or restic.
Here is where the per-terabyte numbers matter. B2 sits around 6 dollars per terabyte per month. Wasabi charges roughly 7 dollars per terabyte per month but bundles egress, meaning downloads are free. The hyperscalers (AWS S3, Google, Azure) look similar on storage but stack fees for retrieval and API calls that can double a restore bill.
| Data size | B2 (approx/mo) | Wasabi (approx/mo) | Yearly (B2) |
|---|---|---|---|
| 1 TB | $6 | $7 (1TB min) | ~$72 |
| 4 TB | $24 | $28 | ~$288 |
| 10 TB | $60 | $70 | ~$720 |
Notice the shape. At 1TB, cloud is almost free money. At 10TB, you are paying 700 dollars a year forever, which is more than a whole second NAS costs.
A second NAS offsite: high up front, cheap forever
This is my favorite for anyone above 4TB, and it is what I run at home. You buy a small NAS, load it with drives, and leave it at a relative's house. Your main unit syncs to it over the internet each night.
The cost is almost all up front. A two-bay unit like a Synology DS224+ runs about 300 dollars, and two 8TB drives add roughly 320 dollars, so call it 620 dollars for 8TB of usable mirrored space.
After that, the running cost is electricity. A two-bay NAS with spinning drives pulls around 20 watts, which is about 4 to 5 dollars a month on a typical US power bill.
The five-year picture
Spread that 620 dollars over five years and add electricity, and you land near 12 dollars a month all-in for 8TB. Compare that to roughly 48 dollars a month on B2 for the same capacity, and the second NAS wins hard on volume.
The catch is trust and logistics. You need a willing host, a power outlet you can borrow indefinitely, and a plan for when a drive fails 40 miles away.
Rotating external drives: cheapest cash, priciest habit
The old-school method still works and is the cheapest on paper. You buy two external drives, keep one plugged in for backups, and swap them, taking the spare to work or a relative's place every week or two.
An 8TB external drive runs about 130 dollars, so two of them is 260 dollars, one time. That is 8TB of offsite protection for less than half a year of cloud at that size.
There are no monthly fees at all. The cost is entirely paid in your attention.
Where this quietly fails
The first time I relied on this, I forgot the swap for six weeks. My offsite copy was six weeks stale, which meant six weeks of new photos existed in exactly one place.
Rotating drives also give you no versioning unless you configure it deliberately, and USB drives are the least reliable storage class there is. I have had two die inside three years. Treat this as a supplement, not your only offsite layer, unless your data is small and you are genuinely disciplined.
Putting the numbers side by side
Here is the honest five-year cost for a common 8TB household, which covers a lot of photo libraries plus documents and some media.
| Method | Up front | Monthly | 5-year total (8TB) |
|---|---|---|---|
| Cloud (B2) | $0 | ~$48 | ~$2,880 |
| Second NAS offsite | ~$620 | ~$5 power | ~$920 |
| Rotating drives | ~$260 | $0 | ~$260 + your time |
The gap is enormous, and it grows every year cloud keeps billing. But the cheapest column is also the one most likely to be out of date when you need it.
How I actually spend the money
For most homes under 2TB, I say pay for cloud and stop thinking about it. Seventy dollars a year buys a hands-off, truly-remote copy, and your time is worth more than the savings.
Above 4TB, the second NAS pays for itself inside 18 months and keeps paying. I run one at my sister's place and cover her the favor by handling her family's tech.
And whatever you pick, follow the 3-2-1 backup rule: three copies, two kinds of media, one offsite. The offsite copy is the one that saves you from the burst pipe, the fire, and the ransomware that encrypts everything on your network at once.
One more thing that saves real money: back up only what you cannot re-create. A 10TB NAS is often 8TB of movies and ISOs you could download again for free, and paying to store those in the cloud is pure waste. Trim to just photos, documents, and irreplaceable files, and a household that looked like a 10TB problem quietly becomes a 1TB one.
That single decision changed my own bill more than any provider comparison did. My real irreplaceable data is about 900GB, so I pay under 6 dollars a month for it and keep the bulky media on a local drive only.
Whatever the sticker price, the copy in another building is the only one that survives the bad day. Buy the cheapest version of that copy you will actually keep current.
Frequently asked questions
How much does it cost to back up a NAS to the cloud per month?
For object storage like Backblaze B2, expect around $6 per terabyte per month, so 1TB is about $6 and 10TB is about $60. Wasabi is slightly higher at roughly $7 per terabyte but includes free downloads. Watch for egress and minimum-retention charges on other providers, which can add 40 to 90 dollars to a large restore.
Is a second NAS cheaper than cloud backup?
Above about 4TB, yes, and it usually pays for itself within 18 months. An 8TB second NAS costs roughly $620 up front plus $5 a month in electricity, landing near $12 a month over five years. Cloud for the same 8TB runs closer to $48 a month with no end date.
Are rotating external drives a good offsite backup?
They are the cheapest option by cash outlay, about $260 for two 8TB drives, and have zero monthly fees. The weakness is that they depend on you swapping and transporting them on schedule, and USB drives fail more often than NAS drives. Use them as a supplement rather than your only offsite copy unless your data is small.
What is the hidden cost of cloud NAS backup?
Egress fees and retrieval charges are the usual surprise. Storage might look cheap, but downloading your data during a real restore can cost tens of dollars on S3-style providers. Some services also bill a minimum retention period, so deleting old backups early still incurs a charge.
How much offsite storage do I really need?
Back up only what you cannot re-create: photos, documents, and anything unique. Re-downloadable media like movies and ISOs usually does not belong in a paid offsite copy. Trimming to just irreplaceable data often drops a household from 10TB down to 1 or 2TB and makes cloud the obvious cheap choice.
