Reallocated, pending and uncorrectable sectors: what they mean and when to replace the drive
CrystalDiskInfo turned yellow and the word "sectors" keeps coming up. Here's what each count means and how worried to be.
The four counts side by side
| ID | Name | What happened | How worried |
|---|---|---|---|
| 5 (05) | Reallocated Sectors Count | A spot went bad and was replaced with a spare. Data was copied across. | Low if small and steady. High if it grows between checks or is in the hundreds. |
| 196 (C4) | Reallocation Event Count | How many times reallocation happened. | Moves with 5. |
| 197 (C5) | Current Pending Sector Count | A spot couldn't be read. The drive waits for it to be written to, then tests it again. | Back up today. Data in those spots may already be lost. |
| 198 (C6) | Offline Uncorrectable | The drive's background surface scan found unreadable spots. | Back up today. |
| 187 (BB) | Reported Uncorrectable Errors | The computer asked for data and the drive couldn't return it. | Back up today. |
CrystalDiskInfo lists IDs in hexadecimal (05, C5, C6), smartctl in decimal (5, 197, 198). They're the same readings.
Why a few reallocated sectors can be fine
Every hard drive leaves the factory with thousands of spare spots, and the platter surface isn't perfect. Swapping a weak spot for a spare is the drive doing its job. Large studies of drive fleets found that drives with any reallocated sectors fail more often than those with none, but many run for years with a small, unchanging count. The useful signal is the trend: write the number down and check again in a couple of weeks.
Can a pending sector go away?
Yes. When that spot is written to, the drive tests it. If it holds data properly, the pending count drops; if not, it's reallocated and count 5 goes up. That's why a full-disk write (for example a full format, or a drive maker's "zero fill") makes pending sectors disappear. It doesn't mean the drive is healthy again; it just means the bad spots were dealt with. Recover your files before doing that, because writing over the spot destroys whatever was there.
What to do
- Copy what matters first, newest and irreplaceable files before everything else. Don't run defrag, chkdsk /r or long scans on a drive that's getting worse; they make it read every sector.
- If files won't copy, tools like
ddrescueskip the bad spots and come back to them later, which is gentler than copy-paste. - Run a long self-test (
smartctl -t long) once your data is safe. If it fails, replace the drive; it's usually still under warranty if the maker's tool also reports a failure. - Clicking or grinding on top of any of these: power it off. That's mechanical, and every minute running makes recovery harder.
The Wirebook drive check-up lesson shows this with Grandpa Spinner: patched knees are reallocated sectors, wobbly spots are pending ones.
Related
How to check drive health · Drive clicking or beeping · "You need to format the disk"
Questions
Is one reallocated sector bad?
Not on its own. Note the number and check again in a few weeks. If it stays the same, the drive is probably fine for now; if it climbs, plan a replacement and keep backups current.
How many reallocated sectors is too many?
There's no official number. A count that keeps rising is the real warning. Dozens to hundreds, or any pending sectors alongside, means back up and replace.
Why does CrystalDiskInfo say Caution?
Usually because reallocated (05), pending (C5) or uncorrectable (C6) is above zero. It turns yellow at the first one, which is deliberately cautious.
Will formatting fix bad sectors?
A full format can clear pending sectors by forcing the drive to retest or replace them, but it erases your data and doesn't make a failing drive healthy. Copy your files first.
Published .