How Do You Check a Hard Drive's Health (SMART)?

Sourced from real discussions on r/DataHoarder and r/buildapc, cross-checked against live PricePerGig listings.

A few high numbers in your SMART data aren’t necessarily bad; rising numbers are bad. If you’ve used and ran the disk for 2 weeks and the numbers are stationary, the drive is fine and no need to replace. If, however, the numbers are changing, start looking for a new drive ASAP.

The only sure fire way to know if a drive is failing or not, or has already failed, is to use a disk checking tool like HD Tune on Windows or smartmontools on Mac/Linux, but this can take hours or even days. If you’ve used the drive for a few weeks already, and noticed the numbers creeping up, it’s probably on the way out.

Buying a used drive is fine, I just recommend always choosing a seller that accepts returns (remember if it’s too good to be true, it probably is!), that way you can test the drive out from top to bottom and just send it back if there are any problems; do not trust that screenshot shown on the listing, that was likely for the 8th drive the seller sold and the best of a bad bunch! Test it yourself using the free tools mentioned here.

The table above shows live used SATA HDD prices on your marketplace, over 4TB, for when SMART tells you it’s time to replace one.

What SMART actually is

SMART stands for a self monitoring system built right into the drive.

The drive watches itself. It tracks errors, remapped sectors, temperature, hours run and more, then stores it all in a little table.

You just need a tool to read that table out. The drive has already done the hard work of recording it.

The numbers that actually matter

SMART throws a lot of values at you. Most you can ignore. Focus on these.

• Reallocated sector count. Bad sectors the drive has swapped out for spares. Zero is ideal. A rising number is a warning.
• Current pending sector count. Sectors that are failing and waiting to be dealt with. This one is serious, especially if it climbs.
• Power on hours. Not health exactly, but it tells you the true age of a used drive.
• Uncorrectable sector count. Errors the drive could not fix. You want this at zero.

A healthy drive shows zeros across the bad-sector values. A few is not the end of the world. A growing pile means back up now.

How to read it

You do not need to be technical. Grab a free tool.

• On Windows, a popular free utility shows the full SMART table and a simple health rating.
• On Linux, the standard smart monitoring toolkit reads it from the command line.
• On a NAS, the dashboard usually shows SMART health per drive.

Plug the drive in, open the tool, and look at the values above. Two minutes of work.

Checking a used drive on arrival

This is the big one, and it is exactly why these pages keep mentioning it.

When a used or refurbished drive lands, read its SMART data straight away.

Check the power on hours to learn its real age, and scan the reallocated and pending sectors. If they look ugly, return it within the warranty window. That window is the whole reason you bought from a proper seller.

A clean SMART report on arrival means you got a good one.

The bottom line

Checking a drive’s health means reading its SMART data with a free tool and looking at the bad-sector counts and power on hours.

Zeros are great, a few are fine, rising numbers mean replace it. Do this on every used drive the day it arrives and on your important drives every so often, and a failing drive will never catch you by surprise again. When one does need replacing, the live table above has your next drive ready.

Remember, SMART data is just an early warning system, if the numbers are rising, then start looking for a replacement now, and buying used is OK, check out the great used selection on eBay.

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