The number that says a hard drive is too old isn’t its age, it’s this

The 1TB hard disk on my laptop has been spinning for close to 20,000 hours. Honestly, almost every rule of thumb tells me it’s overdue, so I’ve half expected it to die for a while now.

However, I decided to stop waiting for it to fail and query the drive itself. I got an answer, and was surprised it was not its hours, power-on cycles, or health badge. The biggest tell came from a number most people will overlook.

19,446 hours was alarming

What reallocated sectors reveal that power-on time can’t

Drives use tiny blocks called sectors to store data. Over time, some of them may become unreliable. If this happens, the drive can replace it with a spare sector and internally remap the address.

The running tally of such swaps may be presented as SMART attribute 05, Reallocated Sectors Count. This value was zero on my Seagate 1TB laptop drive.

Relocation isn’t the same as repairing the original sector. The drive has simply stopped using that sector normally and substituted it with a spare. However, because Windows doesn’t see these internal workings, the number may climb even though your files keep opening normally. You get zero hints from File Explorer.

Hence, why it can be more consequential than the drive’s age. My drive had 19,446 power-on hours, or about 2.2 years of cumulative runtime, and it had been powered on 2,940 times, averaging out to roughly six and a half hours per session.

Judging from the hours and power cycles, I could deduce how much time the drive had spent powered on and roughly how often it was started. They give no context to the state of its sectors, but the reallocated sector count does. It’s the value that records problems your drive has run into.

Hiding in plain sight

The row Windows never shows you

Download and install CrystalDiskInfo, then launch the program. At the top you’ll see a health badge, and underneath that, a table showing SMART attributes. What should interest you is the row labeled Reallocated Sectors Count, ID 05. That’s the number I’d inspect before taking the health badge at face value. For cases when attribute 05, C5, or C6 passes a threshold, CrystalDiskInfo switches it to Caution.

CrystalDiskInfo’s table has some columns that may feel confusing. The scores scaled by manufacturers are in the Current, Worst, and Threshold columns. On my device, these columns on the 05, Reallocated Sectors Count row read 100, 100, and 36 respectively. However, the most important column is Raw Values, and for this particular drive it was “000000000000,” the hexadecimal representation of zero.

An SSD’s relevant health information is different. My WD SN530 reports Percentage Used, which was 0D in CrystalDiskInfo—hexadecimal for 13. My drive reported 13% of its estimated endurance as used. This does not guarantee that 87% of the drive’s lifespan remains.

On Linux, using sudo smartctl -A /dev/sda shows the drive’s SMART data. You’ll want to write down the value you see and today’s date and compare it to any subsequent values you get.

Zero doesn’t paint the complete picture

A number that won’t stay still is the real warning

While zero tells me the drive has not recorded any reallocated sectors in that attribute, it doesn’t guarantee everything will be fine in a month. At the same time, a non-zero value doesn’t mean it’s time to discard the drive. If some values show Caution, it also doesn’t mean your drive is about to stop working.

You should pay more attention to movement. For instance, you may have two drives showing 8 reallocated sectors. Over the next few checks, if the first reads 8, 8, and 8, you can assume the drive had a problem in the past and hasn’t recorded another reallocation since. If the second reads 8, 17, 42, this points to degradation; a drive constantly running into sectors it can’t trust.

The large-scale SMART analysis by Backblaze is another reason why I don’t believe one number is a verdict. It found that some SMART warnings are strongly associated with failure, while also noting that a non-zero value does not automatically mean a drive is about to fail. For my own monitoring, that makes a jump from 0 to 20 much more concerning than a single isolated reallocation that stays unchanged.

I also keep an eye on the Current Pending Sector Count (C5) row. This covers the sectors that haven’t been remapped even though the drive may be struggling to read from them. Those sectors may finally become reallocated sectors, but they can also recover; the count was zero on my drive.

It’s more useful to know whether a drive is still finding new bad sectors than to rely on a single total of bad sectors.

Hard drive age isn’t a verdict

I now have my own rule of thumb.

It’s possible for a drive to fail without warning, so I also avoid treating the evidence it presents as a forecast. It’s important you make copies of the data you value the most without waiting for a warning.

For now, my Seagate still serves me. The Raw Values count remains zero. If the Raw Values begin to climb, I will stop treating this drive as a long-term keeper.