What Does "Reallocated Sector Count" Mean?

Reallocated sector count is a S.M.A.R.T. metric that tells you how many bad sectors your hard drive has found and quietly moved to a reserve area. When a hard drive detects a sector it can no longer read or write reliably, it "reallocates" the data to a spare sector and marks the original as unusable. A small number of reallocated sectors is common on older drives. But when that count starts climbing, your drive is telling you something important: it's failing. The surface of the platters is degrading, and the problem will only get worse over time. If you're seeing this warning, your first priority should be backing up everything on that drive immediately.

We see drives come through our lab every single week with elevated reallocated sector counts. Some people catch it early and save their data. Others ignore the warning for months and show up with a drive that won't spin up at all. The difference between those two outcomes usually comes down to understanding what this metric actually means and acting on it fast.

What Is S.M.A.R.T. and Why Does It Matter?

S.M.A.R.T. stands for Self-Monitoring, Analysis, and Reporting Technology. It's a monitoring system built into virtually every modern hard drive and SSD. Think of it as your drive's internal health dashboard. It tracks dozens of different metrics, from temperature to read error rates to spin-up time, and stores that data in a small reserved area of the drive's firmware.

Your operating system doesn't show you S.M.A.R.T. data by default. You need a third-party tool to pull it up. But the data is always there, running in the background, keeping track of how your drive is performing over its lifetime.

Not all S.M.A.R.T. attributes are created equal. Some, like power-on hours, just tell you how long the drive has been running. Others are critical failure indicators. Reallocated sector count falls squarely in that second category. Along with current pending sector count and uncorrectable sector count, it's one of the three S.M.A.R.T. values that reliably predict drive failure.

A study by Google's data center team analyzed over 100,000 drives and found that drives with even a single reallocated sector were significantly more likely to fail within 60 days than drives with zero. That single data point should tell you how seriously to take this metric.

Reallocated Sectors Count Explained

A sector is the smallest unit of storage on a hard drive. Each sector holds a fixed amount of data, typically 512 bytes on older drives or 4,096 bytes (4K) on modern Advanced Format drives. A single 1TB hard drive contains roughly two billion 512-byte sectors. That's a lot of tiny storage locations.

Over time, some of those sectors will develop problems. The magnetic coating on the platter might degrade. A microscopic piece of debris might scratch the surface. A power surge might corrupt the data stored in a particular location. When the drive's firmware detects that a sector can't be read or written to reliably, it performs a reallocation.

The S.M.A.R.T. attribute for reallocated sector count is typically listed as Attribute ID 05 (sometimes written as 0x05). It tracks the raw number of sectors that have been moved from their original platter locations to the drive's spare sector pool.

Every hard drive ships from the factory with a reserve pool of spare sectors. The manufacturer knows that some sectors will go bad over the drive's lifetime, so they set aside extras. When a bad sector is detected, the drive's firmware remaps the logical address of that sector to point to one of the spares. From the operating system's perspective, nothing has changed. The data appears to be in the same place. But physically, it's been moved.

Reallocated Sector Count vs. Reallocated Sectors Count: Same Attribute

Different tools label S.M.A.R.T. attribute 05 differently, and the naming trips people up. CrystalDiskInfo displays it as Reallocated Sectors Count (plural). smartctl prints it as Reallocated_Sector_Ct. Some manufacturer utilities and BIOS health screens shorten it to Reallocated Sector Count. Every one of these is the same counter: attribute ID 05, the number of sectors your drive has retired and remapped to spares.

So if you searched for "reallocated sectors count" because that is exactly what CrystalDiskInfo showed you, you are in the right place. Read the value the same way no matter how your tool spells it:

• Raw value: the actual number of remapped sectors. This is the number that matters, and the number this guide uses throughout.
• Current (normalized) value: a manufacturer-scaled score, often starting at 100 or 200, that falls as sectors are remapped. It only fails the attribute when it crosses the threshold, which happens far too late to be your backup trigger.

One more naming quirk: attribute 05 counts reallocated sectors, while attribute 197 counts pending sectors, ones the drive suspects but has not remapped yet. If both are climbing, treat the drive as failing no matter which label your software uses. Our CrystalDiskInfo guide shows where each number lives in the interface.

How Sector Reallocation Actually Works

The reallocation process happens at the firmware level, completely invisible to you. Here's the sequence:

There's one important detail that most people miss. Reallocation usually only happens during write operations. If the drive detects a bad sector during a read, it often doesn't reallocate it right away. Instead, it adds it to the "current pending sector count" (Attribute 197). The sector gets reallocated later, when the operating system or a utility writes to that location again.

That's why you might see your current pending sector count go up before your reallocated sector count follows. They're two stages of the same process.

What Your Reallocated Sector Count Numbers Mean

S.M.A.R.T. tools show two values for each attribute: a "raw value" and a "normalized value." This causes a lot of confusion. Let's clear it up.

The raw value is the actual count. If it says 5, your drive has reallocated 5 sectors. Simple.

The normalized value is a score from 1 to 100 (or sometimes 200 or 253, depending on the manufacturer). Higher is better. The drive starts at the maximum value and decreases as sectors are reallocated. When it hits the threshold value, the drive is considered to be in a pre-failure state.

For practical purposes, focus on the raw value. Here's what those numbers generally indicate:

Raw Value	Status	What to Do
0	Healthy	No action needed. Drive is performing normally.
1 to 5	Early Warning	Start backing up. Monitor weekly. Not yet critical but watch closely.
5 to 50	Concerning	Back up immediately. Plan to replace the drive. Surface degradation is active.
50 to 200	Failing	Stop using the drive. Clone it if possible. High risk of total failure.
200+	Critical	Drive failure is imminent or already in progress. Professional recovery likely needed.

How to Check Your Reallocated Sector Count

Your operating system won't show you S.M.A.R.T. data natively (well, Windows will show a generic "disk health" warning once things get really bad, but that's too late). You need a dedicated tool. We've put together a detailed guide on how to check your hard drive health, and our S.M.A.R.T. data guide explains what every attribute means. But here's the quick version for checking reallocated sectors specifically.

Windows: CrystalDiskInfo

CrystalDiskInfo is free, lightweight, and gives you everything you need. Download it, run it, and it immediately shows all your connected drives with their S.M.A.R.T. data. Look for Attribute 05 in the list. The raw value column shows your reallocated sector count.

CrystalDiskInfo color-codes the overall health status. Blue means good. Yellow means caution (some S.M.A.R.T. thresholds are approaching limits). Red means bad. If your drive shows yellow or red, take it seriously.

Mac: DriveDx or smartmontools

DriveDx is a paid app ($19.99) that provides a clean interface for S.M.A.R.T. data on macOS. For a free option, you can install smartmontools via Homebrew:

Look for the line that says "Reallocated_Sector_Ct" in the output. The RAW_VALUE column is your number.

Linux: smartctl

Linux users can use smartctl from the smartmontools package. Install it through your package manager (apt install smartmontools on Debian/Ubuntu) and run:

The -A flag shows just the attribute table. Find ID 5 for your reallocated sector count.

What Causes Sectors to Go Bad

Sectors don't just randomly go bad for no reason. Something is always driving the degradation. Understanding the cause helps you predict what's coming next.

Age and Wear

This is the most common cause. Hard drives have a finite lifespan. The magnetic coating on the platters gradually weakens over years of use. The read/write heads fly nanometers above the platter surface at thousands of RPM. Eventually, things wear out. Drives that have been running 24/7 for 5+ years will almost always show some reallocated sectors. It's normal aging.

Heat Damage

Hard drives don't like heat. Operating temperatures above 50C (122F) accelerate platter degradation significantly. Drives in poorly ventilated enclosures, laptops with blocked vents, or external drives sitting on soft surfaces that trap heat are all at higher risk. Thermal expansion and contraction also puts stress on the platters and can cause the magnetic coating to develop weak spots.

Physical Shock

Dropping a hard drive, bumping it while it's running, or even placing it on a surface with too much vibration can cause the read/write head to contact the platter surface. That's called a head crash. Even a microscopic contact can damage the platter coating in that area, creating bad sectors. Laptops are especially vulnerable because people move them around while the drive is spinning.

Power Issues

Sudden power loss, voltage spikes, and unstable power supplies can all cause bad sectors. When a drive loses power mid-write, the data being written to a sector can be corrupted or incomplete. The sector itself might not be physically damaged, but the firmware may flag it as unreliable and reallocate it. Cheap power supplies and UPS-less setups are common culprits.

Manufacturing Defects

Some drives leave the factory with marginal sectors that pass initial quality testing but fail under real-world conditions. This is relatively rare with major manufacturers, but it does happen. If you see reallocated sectors appearing on a brand new drive within the first few weeks, that's a warranty claim situation.

What to Do When Reallocated Sectors Appear

Don't panic. But don't ignore it either. Your response should scale with the severity of the situation.

If the Count Is Low (1 to 10) and Stable

A few reallocated sectors on a drive that's 3+ years old is not an emergency. It's a sign that the drive is aging normally. Here's what to do:

1. Back up everything. If you don't have a backup, make one now. Not tomorrow. Now. Copy your important files to another drive or cloud storage. This isn't optional.

2. Monitor the count. Check CrystalDiskInfo (or your preferred tool) once a week. Write down the raw value. If it's the same number week after week, you're probably fine for now. If it's creeping up, move to the next section.

3. Plan your replacement. Even if the drive seems fine today, it's telling you its best days are behind it. Start shopping for a replacement. Consider an SSD for the upgrade. You can check our data recovery pricing page to understand the costs involved if things do go sideways.

If the Count Is Rising

This is the scenario that requires urgency. A count that's actively increasing means the platter surface is actively degrading. New bad sectors are appearing faster than the drive can work around them.

1. Stop writing to the drive. Every write operation puts additional stress on the platters and heads. The more you use the drive, the faster it will degrade. If possible, set the drive to read-only or at minimum stop saving new files to it.

2. Clone the drive. Don't just copy files. Clone the entire drive sector by sector using a tool like ddrescue (Linux) or HDDSuperClone. These tools are designed to handle bad sectors gracefully, skipping problem areas and coming back to retry them later. A regular file copy will stall or fail when it hits a bad sector. A cloning tool will work around it.

3. Replace the drive immediately. Don't wait. The rate of sector reallocation almost always accelerates. What starts as 2 new sectors per week can become 20 per day. Once the spare sector pool runs out, the drive will start reporting uncorrectable errors, and data loss becomes unavoidable.

If the Drive Is Making Unusual Noises

Reallocated sectors combined with clicking, grinding, or beeping sounds is a serious situation. Those sounds mean the read/write heads are physically struggling. At that point, software tools won't help you. Power down the drive and don't turn it back on. Every spin-up attempt risks further platter damage. If you need the data, you're looking at a professional data recovery service.

When You Need Professional Data Recovery

Not every drive with reallocated sectors needs professional recovery. If your count is low and stable, and you can still access all your files, just back up and replace the drive. Problem solved.

But there are situations where professional recovery is the only option:

The drive won't mount or is extremely slow. If Windows is taking 10+ minutes to recognize the drive, or it shows up as RAW/unformatted, the bad sector situation has likely progressed beyond what consumer tools can handle. The drive needs to be imaged in a controlled environment with professional equipment that can manage the head movements and read retries precisely.

You hear clicking or other mechanical sounds. Clicking means the heads are failing. This is a cleanroom job. The drive needs to be opened in a particle-free environment, and the heads may need to be replaced with compatible donor parts. You can learn more about the warning signs in our guide on signs your hard drive is failing.

You've already tried recovery software and it failed. Consumer recovery software works by scanning the file system and looking for recoverable data. But if the drive has significant physical damage, the software can't maintain a stable connection long enough to complete the scan. Professional recovery uses specialized hardware like the PC-3000 and DeepSpar DDI that communicate with the drive at the firmware level and can recover data even from severely degraded media.

The data is irreplaceable. Family photos. Business records. Research data. If losing the files would cause real harm, don't gamble with DIY methods. Every failed attempt at DIY recovery can make professional recovery harder and more expensive. The safest path is to go straight to a professional lab.

At MDrepairs, we work on drives with failing sectors every day. Our lab in New Jersey has a certified ISO 5 cleanroom for cases that require head swaps or platter transplants. We offer diagnostics on every drive, and we only charge if we successfully recover your data. You can see our full hard drive data recovery process and what's involved.

Preventing Data Loss from Failing Drives

The best time to deal with reallocated sectors is before they cause data loss. Here are practical steps that actually make a difference.

Monitor S.M.A.R.T. Proactively

Don't wait for your computer to throw a warning. Install CrystalDiskInfo (Windows) or DriveDx (Mac) and configure it to run at startup. Set alerts for critical attributes. It takes two minutes to set up and can save you from losing years of data.

Follow the 3-2-1 Backup Rule

Three copies of your data. Two different storage types. One off-site copy. This isn't just advice for businesses. If you have photos, documents, or anything you'd be devastated to lose, you need at least two backup locations. An external drive plus cloud storage is the minimum.

Keep Drives Cool

Make sure your drives have adequate airflow. Desktop drives should have a fan blowing across them. External drives should sit on hard, flat surfaces with ventilation space around them. Laptop users should use a cooling pad if they're doing heavy disk I/O.

Use a UPS

An uninterruptible power supply protects your drives from sudden power loss and voltage spikes. A basic UPS costs $50 to $80 and can prevent the kind of power-related bad sectors that lead to data loss. For any system with important data, it's a no-brainer investment.

Replace Drives Before They Fail

Hard drives have a useful life of roughly 3 to 5 years under normal use. If your drive is approaching that age, especially if it's showing any reallocated sectors at all, replace it proactively. A new drive costs $50 to $100. Professional data recovery costs significantly more. The math is simple.

Reallocated Sector Count vs. Other S.M.A.R.T. Attributes

People often confuse reallocated sector count with a few other S.M.A.R.T. attributes. Here's how they differ:

Attribute	ID	What It Means
Reallocated Sector Count	05	Sectors already moved to the spare pool. Permanent record of confirmed bad sectors.
Current Pending Sector	197	Sectors flagged as suspect but not yet reallocated. Waiting for a write operation to trigger reallocation.
Uncorrectable Sector Count	198	Sectors that failed and the data could NOT be recovered, even during reallocation. Data in these sectors is lost.
Reported Uncorrectable Errors	187	Read errors that the drive's internal error correction could not fix. Often correlates with bad sectors.

The relationship between these is sequential. A sector first becomes a "current pending sector" (197). If the drive can reallocate it successfully, it becomes a "reallocated sector" (05). If the data couldn't be recovered during the process, it also counts as an "uncorrectable sector" (198).

Pay attention to all three. A drive with zero reallocated sectors but a high current pending count is about to get worse. And a drive with uncorrectable sectors has already lost data, whether you've noticed or not.

Does Reallocated Sector Count Apply to SSDs?

Sort of. SSDs don't have spinning platters or magnetic sectors, but they do have a similar concept. SSDs use NAND flash memory cells, and those cells wear out after a certain number of write cycles. When a cell fails, the SSD's controller remaps it to a spare cell from the over-provisioned area.

Some SSD manufacturers report this as "Reallocated Sector Count" in S.M.A.R.T. data to maintain compatibility with existing monitoring tools. Others use different attribute names like "Retired Block Count" or "Reallocated NAND Blocks." The concept is the same: storage units going bad and being replaced by spares.

For SSDs, the more important wear indicator is usually the "Percentage Used" or "Media Wearout Indicator" attribute, which tells you what fraction of the drive's total write endurance has been consumed. But if you see reallocated blocks climbing on an SSD, it's the same red flag as on a hard drive. The storage medium is degrading.

Frequently Asked Questions

Can reallocated sectors be repaired or reversed?

No. Once a sector is reallocated, it's permanently marked as bad. The drive will never use that original sector again. There is no software tool, format, or utility that can "fix" a reallocated sector. The physical storage medium at that location on the platter is damaged. Some tools claim to repair bad sectors, but what they're actually doing is triggering the drive to recognize and reallocate pending sectors faster. The count will go up, not down. The only way to get the reallocated sector count back to zero is to replace the drive.

Will formatting my hard drive fix reallocated sectors?

No. Formatting only affects the file system and data stored on the drive. It does not interact with the S.M.A.R.T. system or the defect management tables in the firmware. A full format might cause some pending sectors to get reallocated (because the format writes to every sector), but it won't reduce your count. The bad sectors are physically damaged. No amount of software can fix a physical problem.

How many reallocated sectors is too many?

There's no universal magic number. The trend matters more than the absolute count. A drive with 3 reallocated sectors that hasn't changed in two years is probably fine for now. A drive that went from 0 to 20 in a month is in serious trouble regardless of the "low" number. That said, once you're past 50 to 100, the drive's spare sector pool is being consumed at a rate that suggests widespread platter degradation. At that point, drive failure is not a question of "if" but "when." Back up immediately and replace the drive.

Is it safe to keep using a drive with reallocated sectors?

It depends on the context. If the count is low, stable, and you have a complete backup of everything on the drive, then yes, you can continue using it for non-critical purposes. But never use a drive with reallocated sectors as your only copy of important data. Treat it as a drive with an expiration date. It might last another year. It might fail next Tuesday. If you can't afford to lose what's on it, move that data to a healthy drive.

Does a high reallocated sector count mean my data is already lost?

Not necessarily. Reallocated sectors mean the drive successfully moved data from a bad sector to a good one. If the reallocation worked, your data is intact in its new location. The concern is what happens next. If sectors are going bad at an increasing rate, eventually the drive will run out of spare sectors, and new bad sectors will cause actual data loss. Or the heads or motor could fail as part of the same overall degradation. The data isn't gone yet, but the window to get it backed up is closing.

Why did my reallocated sector count jump suddenly?

A sudden spike usually points to a specific event rather than gradual wear. Common causes include the drive being bumped or dropped while powered on, a power outage or voltage spike, extreme heat exposure, or a batch of marginal sectors that all crossed the failure threshold around the same time. Whatever the cause, a sudden jump is more concerning than a gradual increase because it suggests an acute problem rather than normal aging. If your count jumped by 10 or more in a single day, back up the drive immediately and stop using it for anything important.

Can I check reallocated sector count on an external hard drive?

Yes, but it depends on the enclosure. S.M.A.R.T. data passes through the USB or Thunderbolt bridge chip in the external enclosure, and not all bridge chips support S.M.A.R.T. passthrough. If CrystalDiskInfo or your monitoring tool doesn't show S.M.A.R.T. data for your external drive, you can remove the drive from the enclosure and connect it directly via SATA to your computer. Most external drives are standard 2.5" or 3.5" drives inside a plastic case. A few (especially portable SSDs) use soldered connections and can't be removed.