Your own NAS or the cloud: which costs less for backups?

Your hardware and your data

Worked example: 10 TB on two mirrored Seagate IronWolf Pro 20 TB drives, the NAS's price not yet entered. Change any field and every figure follows.

What a NAS at home does not do

A NAS in your home or office is one place. A fire, a flood, a theft or ransomware that reaches the shared folders can take the NAS and the computers it protects at the same time. The 3-2-1 rule asks for three copies on two kinds of storage with one copy somewhere else, which is why the third tile adds the cheapest cloud copy to your own hardware.

Restoring from a NAS on your own network costs nothing and runs at your network's speed. From the cloud, the month you download everything costs more than a normal month, and the download takes as long as your connection needs: the restore time calculator works it out for your speed, and the restore cost guide compares the vendors.

Redundancy inside one NAS protects against a failed drive, not against deleting the wrong folder. Keep versions or snapshots, and for the offsite copy consider immutable storage that nobody can delete before its date. To see how retention and daily changes grow the space you need, use the backup capacity planner.

Where the figures come from

• Seagate IronWolf Pro 20 TB: $879.99 on the maker's own store, checked 11 October 2026; 7.7 W average operating power and a 5-year warranty, from its datasheet.
• Seagate IronWolf Pro 24 TB: $1,059.99 on the maker's own store, checked 11 October 2026; 7.8 W average operating power and a 5-year warranty, from its datasheet.
• WD Red Pro 20 TB: $1,209.99 on the maker's own store, checked 11 October 2026; 6.1 W average power, read and write and a 5-year warranty, from its datasheet.
• WD Red Pro 24 TB: $1,454.99 on the maker's own store, checked 11 October 2026; 6 W average power, read and write and a 5-year warranty, from its datasheet.
• Synology DS925+: 12.33 W with its drives asleep and 37.91 W working, as Synology measures it with all 4 bays full of its own 12 TB test drives (how Synology tests).
• Synology DS1825+: 18.34 W with its drives asleep and 60.1 W working, as Synology measures it with all 8 bays full of its own 12 TB test drives (how Synology tests).
• Drives failing each year: 1.41%, the lifetime annualized failure rate of 353,041 drives in Backblaze's data centers to 30 June 2026, from Backblaze Drive Stats for Q2 2026 (published 29 September 2026). Source: Backblaze.
• Electricity, United States: $0.1831 per kWh, average residential price, July 2026, from U.S. Energy Information Administration.
• Electricity, European Union: €0.2896 per kWh, average household price with taxes, second half of 2025, from Eurostat.
• Electricity, Great Britain: 26.32p per kWh, price cap unit rate for Direct Debit, plus 54.83p a day standing charge, 1 October to 31 December 2026, from Ofgem.
• Cloud prices: each vendor's own price page, as on the calculator; the cloud year is eleven normal months with no downloads and one month in which all the data is downloaded, among offers ready to download within 12 hours.

Drive and NAS power are the makers' own figures, not our measurements. A NAS spends much of its time idle between backups, so a real bill is often lower than the working figures used here.