Hard disks store the data on most of the computers, laptops and external drives we use. On these devices, data is read and written in sectors — the smallest units of storage on the disk, usually 512 bytes or 4 KB each.
With physical damage, software and home repairs can make the case worse. In those cases, hard drive recovery is done in a lab, starting with a free diagnosis.
However, hard disks can run into problems. When they are damaged — by a drop, a power problem or an electronic fault, for example — they can develop bad sectors. If this happens to one of your devices, you will probably have trouble accessing the data stored on it.
But don’t worry: in many cases it’s possible to recover the data from the disk. Let’s take a closer look at what bad sectors are and how to deal with them.
What is a bad sector?
A bad sector is a defective area of a disk that can no longer be read from or written to reliably.
A disk is divided into millions of sectors that store data. They work like small “drawers” that hold the data, which the read/write heads access as the platters spin.
If a sector is defective, the data in it may become inaccessible. When the computer tries to read it, it usually freezes or slows down, and error messages may appear when you start the system or try to open or save files.
Many people use the term “bad block” as a synonym for “bad sector”, but they’re not quite the same. A block is a group of several sectors, so a bad block contains one or more bad sectors, while a bad sector is a single defective unit.
What causes bad sectors on a hard disk?
Bad sectors can have several causes. They tend to become more frequent as the disk nears the end of its useful life or when it isn’t used and handled with due care.
These are the main causes of bad sectors:
Software errors and operating system failures
Software errors, operating system failures, malware, corrupted firmware or unsupported drivers can leave sectors with inconsistent data. These are “logical” bad sectors: the surface of the disk isn’t damaged, but the sector can’t be read correctly.
Faulty read/write heads
When a disk’s read/write head fails, it can touch the platter and physically damage its surface. This creates bad sectors and puts the stored data at risk — and the damage spreads if the disk keeps running.
Drops, heat or water
Disks can also develop bad sectors when the computer is dropped, overheats or gets liquid inside. That’s why you should be careful when using and handling your devices.
Power problems
Power fluctuations or a sudden power cut can cause electronic faults and corrupt data. Bad sectors can also appear when you force the computer to shut down instead of using the normal shutdown option.
Manufacturing defects
The disk may also have manufacturing defects that affect how its components work. Over time, this can damage sectors of the hard disk.
Can data be recovered from a drive with bad sectors?
When a sector goes bad, you probably won’t be able to access the data in that area normally, and it will need a recovery process.
All modern hard disks have a mechanism called “remapping” (sector reallocation), which keeps the disk working by moving defective sectors out of use.
When the disk’s firmware detects a defective sector, it stops using it and redirects reads and writes for that address to a spare sector, so the system no longer runs into the faulty area.
The spare sectors are in a reserved area of the disk set aside for this purpose. If the data in the defective sector can still be read, it is moved to the spare sector; if it can’t, that data is lost from that location. Either way, the physical defect itself isn’t repaired.
This can happen many times over the life of a disk, whenever the firmware finds bad sectors. But a disk with a growing number of bad sectors is a warning sign: the reserved area is limited, and a fast-growing count usually means the disk is failing.
So when you can no longer access your data, you need to turn to data recovery — especially if the number of bad sectors keeps growing.
Can I use software to fix bad sectors on my hard disk?
There are tools that deal with bad sectors. Windows’ own CHKDSK command, run with the /r option in the Command Prompt, looks for bad sectors, marks them so they’re no longer used and tries to read whatever data it still can. But it writes to the disk and forces it to read every sector, which can make things worse on a disk that is physically failing.
Data recovery software is also commonly used. These programs don’t fix bad sectors: they read the disk and copy the files they can find to another drive. In some cases, that’s enough to recover the data.
However, you need to know how to use this software, as mishandling a failing disk can cost you all your data — scanning a disk with physical damage for hours can make the damage worse. In addition, free versions often have limits that stop you recovering all your data, so you may need to buy a paid license.
In more complex cases, data recovery software is often not enough. Bad sectors are frequently caused by physical problems that require parts, such as the read/write heads, to be replaced in a clean room, and the disk to be cloned with specialized equipment — work that only specialized professionals can do.
That’s why the best way to recover data from a disk with bad sectors is to go to a company that specializes in data recovery, such as Bot.
Our experienced professionals use the right equipment in controlled environments, so your data is recovered safely and with much better chances of success.
What should you do if your disk has bad sectors?
So, if your disk has bad sectors, do you know what to do? Here are the main steps you should take:
Write down any other symptoms
Note the symptoms the disk and computer are showing. Check whether there are strange noises, whether the system slows down or freezes, whether the device is recognized, whether error messages appear, and so on.
Keep the hard disk switched off
Once you notice signs of a disk problem, switch it off and leave it off. If you keep using it, you could cause even more physical damage — and if a read/write head is faulty, the damage gets worse every time the disk runs.
Contact a data recovery company
To recover data from a disk with bad sectors, contact a specialized company. Your device will be in the hands of experienced professionals who have handled many cases like yours and know how to identify the fault correctly.
These companies also use professional data recovery tools, the right equipment and controlled environments to handle devices safely.
Bot is a company specializing in data recovery, with more than two decades of experience. You can choose free collection from your address (islands not included) or take your device to one of our reception points in Lisbon, Coimbra, Porto and Braga. Our team will carry out a free diagnosis of your device and send you a quote within 48 hours.
Get in touch on any of our channels: Instagram or Twitter. We offer 24/7 support and we’re here to help!
Need to recover the files? Bot runs a free diagnosis in its lab: see our hard drive data recovery service.
