How is the data stored on HDDs and SSDs?
In HDDs the bits of data (all those 1s and 0s of binary code) are stored on the magnetic layer of the platter(s) and are read and written by a number of heads that "float" above the surface of a rotating disk. Over time, these bits may flip their magnetic polarity and that could cause data corruption. However, an HDD usually has a special error-correcting code (ECC) that detects errors and corrects them, if possible.
A solid-state drive (SSD) doesn't have moving parts and stores data in special cells on a chip. All these cells are separated with an insulating layer to keep charged electrons inside. Eventually, the insulating layer may degrade and the charged electrons may leak out, causing data loss.
As for the lifespan, an SSD has a relatively shorter one due to a limited number of write cycles (up to 100,000). On the other hand, an HDD consists of moving parts, so the chances that one of those parts fails and causes data loss are higher compared to solid-state drives.
What could cause data loss from external hard drives?
Additionally, both HDDs and SSDs can lose data because of:
- accidental drive formatting or deletion of files;
- physical damages (exposure to extreme temperatures, magnetic fields, high humidity, shocks, fire, etc.);
- power surge or power outage;
- file system or partition corruption;
- software malfunction;
- virus attack or spyware infection.
The problem resides not in the fact that external drives can fail, but in the fact they could fail unexpectedly. So, backing up files regularly is the best practice, regardless of the drive type. Additionally, to minimize the risks of data loss, you’d better:
- partition your external hard drive (in other words, create separate program and data zones, so when the program "part" crashes, it will still be possible to recover the user’s data stored in a separate location);
- perform disk defragmentation (only in case of HDDs) to get the files arranged more contiguously and speed up the functioning of your PC;
- use an antivirus software on your computer and update it regularly;
- try to avoid connecting an external storage device to a computer, when you’re not sure if it has any anti-virus protection at all;
- use a surge protector;
- avoid deleting a file if you don’t know what it is used for, especially a system one;
- keep your external hard drive in a dry, well-ventilated and safe place;
- try to avoid dropping an HDD or turning it over while it’s working and right after unplugging it safely from a PC;
- connect external hard drives using only their native cables (or cables of a reliable brand);
- avoid plugging an external hard drive into a damaged or not working USB slot of the computer, as this might destroy both devices.
What are the chances to recover files from an external HDD and SSD?
When discussing data recovery, it is important to distinguish between external hard disk drives (HDDs) and solid-state drives (SSDs). As mentioned earlier, their internal architectures differ significantly, which affects not only how the data is stored, but also the drive’s behavior after data loss.
External hard disk drive (HDD)
The chances of successful data recovery from an HDD depend on a number of factors, in particular, on the issue that caused data loss. Such drives store data on spinning magnetic platters, which can be prone to mechanical failures. Usually, physical damages could be recognized by clicking sounds and other strange noises. Let’s make it clear, it’s ok when a hard disk drive makes some noise, especially when it’s booting or accessing/copying data, but the sound should be low-pitched and unobtrusive. In case an HDD produces a grinding or persistent clicking noise, if it keeps vibrating or beeps once and stops humming, that might be a sign that there's something wrong with it. So, if you happen to notice any kind of mechanical damage to an external hard drive, you’d better contact a data recovery center as only a qualified specialist can evaluate the extent of damage and restore data without making it even worse.
On the other hand, when you delete some files by mistake, quickly format your disk or encounter a logical failure like partition or file system corruption, the possibilities to restore deleted or lost information are usually quite high (at least, before it’s overwritten). Yet, they depend on the file system type of your HDD, as it determines the way the files are deleted from a device. Most external hard drives have NTFS, APFS, FAT32 or exFAT. So, the chances of successful data restoration may vary from almost 100% in case of NTFS to rather moderate in case of FAT32 or exFAT, when, as a rule, only a partial recovery of lost information is possible due to extensive file system fragmentation. APFS can further complicate recovery because of its widespread use of encryption, which protects both data and metadata.
External solid state drive (SSD)
Solid-state drives are generally more durable and less prone to physical failure than HDDs. However, they store data on flash memory, which is managed by a special internal controller. Many of these controllers implement TRIM, a feature designed to improve performance and prolong the drive’s lifespan. When a file is deleted or the drive is formatted, TRIM tells the SSD that the blocks used by that data are no longer needed. The drive can then mark those blocks as free and eventually erase them through a process called garbage collection.
Because TRIM removes references to deleted files almost immediately, recovering data from an SSD is usually impossible once it has been deleted or the drive has been formatted. However, there are situations when TRIM is not triggered, so data recovery may still be possible:
File system corruption or logical errors. If the drive experiences an issue, the TRIM command may not be executed, leaving the data physically present.
TRIM is disabled or unsupported. Some external SSDs connected via USB, USB-C or Thunderbolt do not support TRIM, or the host operating system may be unable to send TRIM commands to external drives.
Older or budget drives. Certain SSD models lack full TRIM support or do not implement it properly.
Without TRIM, recovery chances can approach those of HDDs, although some nuances of flash memory management may still affect the outcome.
Regardless of whether the device is an HDD or SSD, following these precautions is crucial:
Stop using the drive immediately after detecting data loss. Continued use can overwrite the files.
Avoid formatting or repairing the drive using system utilities before attempting recovery. Such operations may destroy recoverable data.
Connect the drive directly to a computer using a reliable interface (USB, USB-C, Thunderbolt, etc.), rather than through a media player, console or other intermediary device.
Avoid moving or shaking the drive. HDDs must be handled with extra care, as their platters and read/write heads are very sensitive to mechanical shock. Make sure that you keep the drive on a stable surface during recovery.
Do not save recovered files back to the same drive. Use a separate storage medium to prevent overwriting.
Do not attempt to repair physical damage on your own. Drives with broken connectors, failed controllers or water damage should be handled by professional in-lab services.
Following these guidelines will help to preserve recoverable data and prevent accidental overwriting. Yet, to achieve the best possible outcome, using reliable professionalgrade tools is highly recommended. Professional data recovery software developed by SysDev Laboratories works with a wide range of file systems and storage types, offering advanced scanning and reconstruction capabilities to maximize the chances of successful data recovery from external HDDs and SSDs, even in challenging scenarios.