How much time until an unused hard drive loses its data?

The conventional wisdom is that you should revisit your data every five years to make sure that you can still read it. The general consensus is that the magnetic platters in the drive will start to degrade in 5 years of storage. The bigger issue is that storage technology changes. That means a format that works today will be unreadable 5-10 years from now.

The best option you really have is to have multiple copies on multiple formats and to check on the data at least once or twice a decade. That's really the only way to make sure that the data is both intact and on a format that can still be read.

If you can afford it, you could always pay someone else to manage it. Services like Carbonite can store lots of data for long periods of time. They also can provide disaster recovery services in case your loose your computer and local backups.

Hope this helps

The data on the HD will last much more than two years, so there is a very good chance you can recover it.

The only problem might be that new hardware could be incompatible with old hardware, but two years isn't long at all.

I bought a very old Zenith 386 system with an RLL full-height hard drive, circa 1987 at a local thrift store for $5. Had 640KB of RAM and a 386 CPU.

Before you had IDE hard drives, you had MFM and RLL drives; these did not have the controller electronics on board but had ribbon cables that went to an ISA controller card. Very old drive.

Plugged it up, got it to boot (after figuring out the "BIOS drive type" - it was something like 70MB) just fine. Had MS-DOS 5.0 installed. Scandisk revealed 1 bad sector on the drive. Might have been caused due to movement, this is from the era where drives didn't lie about their bad sectors (and had a "defect table" sticker on it).

So I imagine if they are in climate controlled conditions and not subject to shock or vibration that they would last quite a long time.

Hard drives fail and are not good long term storage devices. but you do not need to rewrite anything on them...

if you want to keep data over long periods of time, get a magnetic tape drive (they are used by large companies for their data)

Hard drives, flash storage and CDs will generally last around 10 years max, magnetic tapes can last for 50 years and possibly longer.

source: https://www.pcmech.com/article/how-long-does-backup-media-last/