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Hard Disk Drives versus Solid State Drives

Hard disk drives (HDD's) and solid state drives (SSD's) are two forms of non-volatile storage used in computers. "Non-volatile" means that when the system and the drive are working properly, the data on the drive remains there until the user or the system intentionally deletes it. This is true even when the computer is powered down, and even if the drive is removed from the computer.

Until rather recently, HDD's were the only non-volatile used in most computers. Early SSD drives were too slow, too small in terms of capacity, and two expensive per unit of storage to be practical for uses other than portable storage (for example, as flash drives or SD cards).

That is no longer the case. Although still more expensive per unit of storage than HDD's, SSD's have come down enough in price to be affordable as the primary non-volatile storage media for both desktop and laptop computers.

The speed of SSD's has also improved phenomenally, to the point that they are much faster than even the fastest and best HDD's. Simply replacing a computer's HDD system drive with an SSD drive can reduce the boot time from minutes to seconds, and allow programs to load almost instantaneously, assuming that the machine also has adequate processor and RAM resources.

As if incredible speed weren't enough, SSD's also consume less power and produce less heat than HDD's, and are less susceptible to damage from jostling because they have no moving parts. All of these advantages have led many people to believe that SSD's are "better than" HDD's. But is that always true?

Let me explain that to you.


Advantages and Disadvantages of Hard Disk Drives

Cut away view of a hard disk drive showing the disks and other parts inside

Let's start our discussion of the relative advantages of SSD's and HDD's as storage media by taking a look at hard disk drives and how they work.

A hard disk drive, also called a hard drive or HDD, is an electromechanical device that contains spinning disks to which data is magnetically written and from which it is read. HDD's are inexpensive and are available with huge storage capacities.

The spinning disk system of a hard drive imposes immutable limits on how quickly data can be written or read. It also causes HDD's to be sensitive to physical shock, especially from jostling, vibration, or other movement while they are in use; as well as to ordinary wear that affects all devices with moving parts. HDD's also use much more power than SSD's do.

On the other hand, because the data is written magnetically (the actuator arms and heads ride on a layer of air and never actually touch the disk), the magnetic coating of a quality hard disk can be written and re-written to pretty much indefinitely. It's the mechanical parts of the drive, not the magnetic coating, that are subject to failure due to wear.

Unless the mechanical parts of the drive fail in a way that physically damages the disk coating (for example, if the heads actually touch the disks in any way), the data from a failed hard drive is almost always recoverable by professional data recovery companies. It can be expensive, but it's almost always possible.

Conversely, it's also easy to reliably and securely delete a file from a HDD using a secure deletion utility, making it permanently irrecoverable by any means, without causing any harm to the rest of the data on the drive.

In summary, the advantage and disadvantages of hard disk drives are:

Advantages of HDD's

Disadvantages of HDD's



NAS hard drives are a subset of HDD's designed to be used in Network Attached Storage (NAS) devices,commercial data centers, and high-availability servers. These devices typically run 24 hours a day, often under extremely heavy input/output loads, and usually contain multiple tightly-packed hard drives in various RAID configurations.

NAS hard drives are designed to be durable enough to handle that kind of use. They also are designed to run cooler, use less energy, and produce less vibration than desktop hard drives. All of these factors are important in environments in which hundreds or thousands of hard drives may be in use simultaneously.

In addition to their intended use in NAS devices, NAS hard drives are a good choice for use in external hard drive enclosures, home media servers, desktop computers used for serious multimedia editing or CAD/CAM applications, and video surveillance recording systems that use hard disk drives.

In a nutshell, NAS drives are a good choice for drives that will be working very, very hard.

One thing you should not expect from a NAS hard drive installed in a desktop computer is more speed. NAS drives, as a group, are no faster than high-quality desktop drives of the same spindle speeds (5400 RPM or 7200 RPM), and are much slower than SSD drives. Remember that NAS hard drives are designed for use in NAS devices where the network connection is usually the slowest link in the chain. Even a 5400 RPM SATA drive is faster than a typical NAS enclosure.


Advantages and Disadvantages of Solid State Drives

Two point five inch Crucial S A T A hard drive

Solid state drives, or SSD's, are a type of non-volatile storage that use transistors on a NAND flash memory chip to store data. They are more expensive than HDD's, especially at higher storage capacities.

Unlike HDD's. SSD's contain no moving parts. They also produce no noise and less heat, consume less power, are much less sensitive to physical shock, and are much faster than HDD drives.

SSD drives are available in several form factors, including 2.5-inch "laptop-sized" drives that can be used as drop-in replacements for HDD's in both desktop and laptop computers. The data on the existing drive typically is copied to the SSD using drive-cloning software or a drive replicator.

In otherwise-powerful computers with fast processors and adequate RAM, replacing the HDD with an SSD is usually the easiest and most cost-effective way to improve the computer's performance. This simple and reasonably affordable upgrade can dramatically speed up a computer, reducing its boot time to seconds, and enabling even large applications to open almost instantaneously.

The biggest downside to SSD's is that they do have very definite limitations on how many times an individual transistor can be written to. Literally every time you write to the drive, you shorten its life a little bit. This makes them questionable choices for constant, extremely write-intensive uses such as video surveillance recording or heavy-duty video editing.

Another downside to SSD's is that to maximize the life of the drive, deleted data is "trimmed" (actually deleted and zeroed, rather than simply having the pointer to the file removed), and writes are "wear-leveled" across the drive so the same transistors aren't written to repeatedly. This does in fact extend the drive's life, but it also makes it difficult or impossible to recover accidentally-deleted data.

Ironically, it's also very difficult to reliably delete selected data that you really do want gone from an SSD. The trim function works when the hard drive is not otherwise busy, so you're never really sure when the data you want gone will be deleted. It's also possible in some cases to recover data from the drive's buffer. These considerations make SSD's questionable choices if dealing with classified or other sensitive data.

If you want to securely erase an entire SSD, however, you can do so using the ATA Secure Erase command or most third-party partitioning software.

In summary, the advantages and disadvantages of solid state drives are:

Advantages of Solid State Drives

Disadvantages of Solid State Drives


NVMe M.2 Solid State Drives

A Crucial N V M E solid state drive

NVMe (Non-Volatile Memory Express) solid state drives are a subset of SSD's that differ from SATA SSD's mainly in their form factor and interface. NVMe drives use the PCIe bus as a data interface. They can connect to an adaptor in a PCIe port, or directly to the motherboard using a special connector known as an M.2 NVMe interface.

A high-quality NVMe SSD in the M.2 NVMe slot of a good motherboard will give you the fastest data transfer available in the world as of the time of this writing. At the time of this writing, theoretical data transfer speeds for NVMe are five times those of SATA. If you are building or buying a new computer, this is definitely one feature you should insist upon.

Other than the interface and the speed, the same advantages, disadvantages, and other considerations apply to NVMe drives as to any other SSD drives.


My Recommendations

Considering the advantages and disadvantages of both SSD and HDD drives, here are my recommendations for readers who are planning to buy or build a new computer, or to upgrade an existing one:

System Drive (Where the Operating System and Applications Will be Installed)

Data Drive (Where Your Documents, Pictures, Videos, etc. Will be Stored)

Whatever drive configuration you choose, remember to back up your computer frequently. No storage system is absolutely reliable, and there are many problems other than drive failures that can cause you to lose your data. When that happens, whether it is an inconvenience or a disaster will depend on whether you have good backups.