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 anti-virus 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.
And once you realize some information has been lost or deleted from your external hard drive, please have a look at the list of rules to take into consideration when trying to recover them. They will help to avoid the crucial errors.
What are the chances to recover files from an external HDD and SSD?
The chances of successful data recovery depend on a number of factors, in particular, on the issue that caused data loss. 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, accidentally 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 of your HDD or SSD, as it determines the way the files are deleted from a device. Most external hard drives have NTFS, HFS+, 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. As for HFS+, the success of the recovery procedure is subject to how long the drive has been used after data deletion.
Please note that if you use an external SSD drive that earlier formed part of a PC, the data recovery would be almost impossible due to the TRIM command enabled by default on the majority of internal SSDs.