Your computer reports bad sectors, a disk tool shows warnings, or files suddenly take forever to open. A drive with bad sectors can still hold all your data, but what you do next decides how much of it you keep.
Here’s what bad sectors are, how to check safely, and which common “fixes” can do more harm than good.
What a bad sector is
A hard drive stores data in tiny units called sectors. A bad sector is one the drive can’t reliably read or write. There are two kinds:
- Logical (soft) bad sectors: the data in the sector is inconsistent, often after a power cut or crash. The surface itself is fine.
- Physical (hard) bad sectors: the surface is damaged or the heads can’t read it anymore. These don’t heal.
Every drive has spare sectors and quietly swaps out a few bad ones over its life. Trouble starts when the number keeps growing. That usually means the surface or the heads are wearing out, and the failure can speed up quickly.
Signs your drive has bad sectors
- Files or folders that take much longer to open, or won’t open
- Copying stops partway with read errors, such as “cyclic redundancy check”
- The computer freezes when it accesses certain files
- Disk tools or SMART warnings report reallocated or pending sectors
- Clicking or repeated retries while reading
For the full list of warning signs, see 5 Signs Your Hard Drive Is Failing.
A safe way to check
Most drives keep a health log called SMART. Free tools can display it without writing anything to the drive. Look at values such as Reallocated Sectors, Current Pending Sectors and Uncorrectable Sectors. Any non-zero value is worth noting. A number that increases between checks is a sign to stop using the drive.
Reading SMART data is a quick, read-only check. Running long tests is a different matter, as explained below.
What not to run on a drive you need data from
- CHKDSK with repair options, or First Aid on a Mac. These tools fix the file system by writing to the drive. On a failing drive they can remove damaged files and folders they can’t read, and they keep the drive working hard for hours.
- Full surface scans and “bad sector repair” tools. They read, and sometimes rewrite, every sector on the drive. On weak heads or a damaged surface, that much reading can push the drive into complete failure.
- Defragmenting. It moves large amounts of data around a drive that’s struggling to read it.
- Recovery software that scans the whole drive repeatedly. Read Is It Safe to Use Data Recovery Software? first.
These tools are built for healthy drives. On a failing one, the extra reading and writing is exactly what you want to avoid.
What to do instead
- If the drive still works well and the data isn’t backed up, copy your most important files first, a few folders at a time, to a different drive. Don’t try to copy everything at once.
- If copying fails, slows to a crawl, or the drive makes noises, stop and power it off. Continuing to retry the same unreadable areas adds wear.
- Don’t write anything new to the drive, including installing software on it.
How a lab handles a drive with bad sectors
Professional recovery uses specialized hardware that reads the healthy areas of the drive first and returns to the weak areas carefully afterward, with control over how many times each area is retried. That gets the most data off before the drive deteriorates further, without writing anything to it.
Disklab is a data recovery lab in St. Louis, on Olive Blvd. You can drop off your device or ship it to us from anywhere in the US.
Disklab recovers data from failing hard drives every day. Seeing bad sector warnings? Start a recovery case or call us at 1-844-347-5522. The evaluation is free, and you pay only if we recover your data.