How to make a reliable NAS cold backup? Don't just sit idle on retired hard drives—I've laid out the pitfalls I've set up for you

I finished writing review of ransomware last year, I reviewed my own defenses in the middle of the night: snapshots and one-way backups, but the actual offline copy was just an old drive lying in a drawer—and the backup on it was still over a year old. It means my hardest barrier is basically useless. This article will clearly explain the pitfalls I made later in the cold backup supplement.

no matter how thorough the online backup is, it's still missing a power-off drive

The three gates on my NAS are layered: the Btrfs snapshot controller accidentally deleted, the old DS220j one-way rsync controller is faulty—I've written about both before. But they share one thing in common—they're all plugged in and online. If ransomware really comes in, theoretically, it can touch every online copy; Accidental deletion is even worse. the time my recycle bin was emptied, I recovered it from snapshots. But what if the snapshot retention period has already passed?

cold backup is a backup for this small probability: a hard drive without power, physically isolated from everything. It doesn't need to be fast; updating twice a year is fine. What matters is "still present when something happens, still readable." the 1 in backup 3-2-1 is exactly what it is.

cold storage disk: retired disks are just right, and tile-stacked disks are actually more suitable this time

Here's something unconventional: I previously advised you not to buy tile-stacked disks as your main NAS because random drafts are too poor. But cold backups happen to be the comfort zone of Stacked Tiles—fill out the order at once, then lie down all year, occasionally reading the whole disk once, and the thing Stacked Tiles fears most—random lowercase letters—is completely out of reach. So after retirement, any reliable driver, whether PMR or SMR, can do this job.

I have this 4T red model that I discontinued when I switched to 8T new model. Before transferring to cooling standby, check the condition: power on for 21,000 hours, Current_Pending is 0, temperature should be kept below 40°C year-round, qualified. Conversely, if SMART already has emerging bad sides, don't use it as a cold reserve—that's treating psychological comfort as insurance.

a quick reminder: if you have retired SSDs on hand, don't just casually use them as backup devices. The mechanical disk is powered off and left unattended, and the magnetic records are very stable; SSDs store data using charge; long-term power outages can cause slow leakage. Household drives only last about a year at room temperature, and the deeper the write, the shorter the wear. The cold backup method, which "writes once and sits for a year," happens to play on its weaknesses, making mechanical drives a more stable choice.

also need a read/write tool: a SATA to USB3.0 hard drive enclosure for about 30 yuan. A 3.5-inch drive must be a box with 12V independent power supply; USB alone is not enough; A USB power supply for a 2.5-inch laptop drive is sufficient, no need for extra power. The box I bought has a power button. After backup, I press the power button to cut off the drive and then unplug the drive, saving me the need for hot-swapping.

capacity calculations: 4 6,000 photos totaling 186GB, backup of two computers, plus system and Docker configuration exports, all packed in under 500GB. A 4TB drive can hold the quarterly version for the next three years. I chose the exFAT format—it reads as soon as Windows and Mac plug in. When it's time to flee, you can easily unbox and pick up any computer. If your environment is entirely Linux and you want to keep permission attributes, ext4 is fine, but the trade-off is that Windows cannot read it by default, so you have to weigh it yourself.

and how to prepare: Directory by date, don't use compressed format

List what to prepare first: photo library, documents, configuration export these three must be kept cold. Movies and series don't need them—things that can be downloaded again don't deserve to take up offline copy; The same applies to Docker mirrors; re-pulling only gives a few gigabytes.

here's a big pitfall I've encountered: at first, I used Synology Hyper Backup to export to this drive, because it has version management and deduplication. Later, when I switched to Feiniu as the main source and wanted to read that backup, I found that the exported .hbk was Synology's proprietary compressed format. Without the Synology machine, you couldn't even view the file list. The correct solution for cold backup is to copy bare files directly —just throw the folder in as is, and any system it can be plugged in is accepted.

directory is layered by date, making old and new instantly distinguishable:

/Cold Backup-2026-03/photos/Cold Backup-2026-03/config/Cold Backup-2026-09/photos ...

Copy command with just one rsync, Install before bed and finish up:

rsync -avh --progress /vol1/photo /mnt/usb1/cold standby -2026-09/

configuration export. Don't forget: Feiniu system backup, Docker compose file, Synology configuration file, Set up a separate config directory. In the first year, I only prepared data but no configurations. On the day of the recovery drill, I manually reconfigured the apps one by one, spending an entire night extra.

preparing without verification, is that the same as unplugging the power and closing the drawer after copying

unprepared? I suggest you do it for ten more minutes. The most insidious part of the backup issue is: just because the copy didn't report an error at the time doesn't mean you can still read it six months later—the disk will quietly break down.

my approach is to back up and generate a checklist in the root directory of the drive:

find /mnt/usb1/cold standby-2026-09-type f! -name SHA256SUMS.txt -exec sha256sum {} + > /mnt/usb1/cold standby-2026-09/SHA256SUMS.txt

Next time you call on for follow-up, enter the directory and run a linesha256sum -c SHA256SUMS.txt, Each file is hashed one by one, and not a single one escapes. The USB 3.0 enclosure tested reading speeds around 110MB/s, with a full 500GB data test lasting over an hour, making it perfect for running at night.

the first thing to do after powering on isn't actually a check, but to check SMART first— if any of those five indicators show up Current_Pending, try to save them before reconciling, and don't keep dragging things down the bad side.

verifying everything is green, don't rush to finish it. I'll do another 'recovery drill': unplug the drive, plug it into the Windows computer, browse a few directories, open a few photos, and confirm that even outside the NAS environment, it still reads the data. Whether cold backup is done correctly only counts after rehearsal—you never know what kind of machine you'll have when you need it.

four key elements of tags. I've suffered from only writing dates

This section seems trivial, but it's actually the pit I fell into the most disheveled. The earliest sticker on that disk had three characters written "2024.03." Six months later, when the power was on, I stared blankly at several catalogs on the disk: Is this full volume or increment? How much different is it compared to online? In the end, I was forced to re-scan the entire palette before confirming.

now labels always have four fixed items:

take photos after writing, save them to your phone album, and search for 'cold backup' to browse anytime. Storage location is also important: place the anti-static bag or original box flat in a dry place, and don't mix it with a key screwdriver in a drawer—if you pull the drawer and the metal parts hit the plate, you'll cry. In winter, bringing it into the room from a balcony without heating and letting it warm up for a long time before turning on the electricity—condensation is much scarier than magnetic fields. The magnets on household speakers are no problem when separated by an anti-static bag.

how often I turn on the electricity, I take it

my routine is once every six months, at most a year. If the mechanical drive is left unpowered and left untouched, the data itself can be stored for ten years without issue. The real concern isn't "just sitting there," but "not knowing if it breaks." So every follow-up is fixed in four steps: power on to check the SMART → run verification checklist→ update it once there are incremental changes→ remove old labels and apply new ones. I casually recorded the visit date in my phone calendar, or else I really would forget. Don't ask me how I know.

the real treasure of home photos, you can go further: rotate between two pallets—one at home, one at your parents' home or office. For disasters like fires and floods, the cold storage drive in the drawer is missing along with the NAS; the one in another location is the real backup. During follow-ups, the two disks were swapped and updated, so the cost was just buying one more disk—worth it. There is no standard answer to

frequency; it depends on how fast your data grows. My photo library adds four to five GB a month, with every six months to prepare. If something really happens, I'll just lose half a year's increase—accepting it. If you use your NAS as a workspace and generate documents every day, you just reduce the cycle to monthly, with the same commands—just a few extra trips.

Here's the order: dig out the retirement disc→ SMART health check→ exFAT → copy the bare file by →date to generate a checklist → label four key elements→ take photos to record the calendar→ and check back after six months. After spending most of the day on one stage, I switched to the reassurance of 'no matter what you do, there's always a way out.'