What are the important characteristics of modern hard drives and what are the differences between various data storage technologies.

In his report Data Age 2025IDC predicted that the needs of data storage would have increased globally to reach the enormous amount of 163 Zettabytes (ZB) by 2025: this is ten times the amount of data produced 8 years earlier (one Zettabyte equals one billion Terabytes).

Already in 2021 Seagate claimed SSD drives wouldn’t kill hard drives: today’s hard disk, designed to meet the needs of different industries, still remain the most commonly used archiving solution. Within their catalogs, the various manufacturers offer hard drives for PCs, NAS systems, video surveillance systems and data centers that differ in terms of interfaces, performance and reliability.

For example, as he explains ToshibaPC and notebook hard drives are typically designed for 8-16 hours of operation per day and an annual workload of 55TB while hard drives for NAS systems, surveillance applications and class products enterprise they need to support 24/7 operation and handle higher workloads.

What is MTTF in the case of hard drives

The sail MTTF is to mean Mean Time To Failure i.e. “Mean time to failure”: this is a measure of thereliability of a hardware component. In the case of hard drives, the MTTF value indicates the average time estimated before the unit malfunctions. If a hard drive has an MTTF value of 1,000,000 hours, this means that, on average, the drive will operate properly for approximately 1 million hours before experiencing a hardware failure.

It is important to note that the MTTF value does not indicate the duration exact of a unit and therefore its life expectancy. While it is true that a hard disk with a higher MTTF value can theoretically guarantee greater reliability, there are many factors that can influence the actual useful life such as how to use it, working environment, operating temperature, the build quality of the hard disk and so on.

Typically, PC hard drives are designed to operate between 0°C and 60°C while enterprise-class hard drives are designed to operate between 5°C and 55°C. THE vendor provide information on shock and vibration resistance: the hard disk per NAS system and enterprise-class ones are less sensitive than hard drives designed for PCs or surveillance systems because they are integrated into a single system. The rotational vibrations can amplify each other: for this reason the NAS and enterprise models integrate special vibration detectors and control mechanisms that record and compensate for these phenomena.

Within data center the MTTF value allows you to make predictions: with a large number of units it is possible to estimate how often i could occur breakdowns. With an MTTF of 1 million hours and 1 million drives, one failure per hour is expected, or with 1,000 drives, one failure every 1,000 hours.

For hard drives operating 24/7, the parameter can be determined Annual Failure Rate (AFR) starting from the MTTF: it is more indicative as a percentage value, as Toshiba explains again. In simpler terms, AFR can be calculated as 8,760 hours of annual operating time divided by the MTTF in hours and multiplied by 100.

An enterprise-class drive with an MTTF of 1.4 million hours has an AFR of 0.625%. In a data center with 100,000 drives, it is expected that 625 of these will fail each year and need to be replaced. If the operator opts for drives with an MTTF of 2.5 million hours, the AFR drops to 0.35% and probably only 350 hard drives will fail in the same period, significantly reducing maintenance visits“, Toshiba experts comment.

Il annualized failure rate o AFR is periodically noted, for example, also from BackBlazea company that uses hundreds of thousands of hard drives in its data centers, even if they are not classy enterprise because they are cheaper and still able to offer excellent reliability over the years. We recently saw the ranking of the best hard drives of 2022 according to BackBlaze.

Differences between the technologies used to store data on hard drives

The different ones type on the hard disk they also often differ in the technology used to record data on the magnetic disks inside the unit. Below is a brief summary of the various technologies available and used in the various hard disk models.

CMR (Conventional Magnetic Recording). It is conventional magnetic recording technology that has been around for decades. With this technology, data is recorded on magnetic disks via read and write heads that write to a magnetized surface. In practice, the head “writes” a series of bits on the magnetic platter, creating a circular trace which is divided into sectors. CMR technology has already reached its limit of 16TB of capacity per single drive.

SMR (Shingled Magnetic Recording). Similar to CMR, it differs in that data is recorded slightly differently. With SMR, in fact, the data are superimposed on each other like the tiles of a roof (hence the name “shingled“). In this case the data writing activities may be slower than in CMR mode but it is possible to increase the data storage density on each magnetic disk.

MAMR (Microwave-Assisted Magnetic Recording). It is an advanced magnetic recording technology that uses high-frequency electromagnetic waves to heat the surface of the magnetic disk while data is being written. This makes it easier for the write head to magnetize the disk, allowing for higher density in data storage.

The writing head manages to focus the magnetic flux by reducing the magnetic energy required for writing: it can therefore be smaller and write bits more densely.

Currently this technology allows to obtain hard disks with a capacity of 20 TB; with progress being completed, drives up to 30TB may be available in the future.

HAMR (Heat-Assisted Magnetic Recording). Similar to MAMR, it uses a laser to heat the surface of the magnetic disk instead of electromagnetic waves. This allows for even greater storage density than MAMR.

HDMR (Heated Dot Magnetic Recording). Even more advanced than HAMR, HDMR uses a laser to create points of magnetization on the surface of the magnetic disc. These dots can be read and written more accurately than the circular traces used by the CMR and SMR, allowing for even higher storage density.

In general, the more advanced magnetic recording technologies (such as MAMR, HAMR and HDMR) allow you to increase the data storage capacity on magnetic disks, but they may also require more expensive and sophisticated hardware.

Writing speed in hard disks: when it tends to decrease

As Toshiba points out, in addition to reliability, the most important factors in the case of hard drives are the performance and the energy consumption.

Hard drives with a rotational speed of 10,500 or 15,000 revolutions per minute (RPM) offer the best performance, even if they have been replaced in recent years with SSD drives. Enterprise-class hard drives a 7.200 RPM deliver sequential throughput up to 280 MB/s and 400 input/output operations per second (IOPS). Values ​​​​that are orders of magnitude lower than those ensured by solid state drives.

The performance of hard disks decreases with the fill level, because the first-write and external data tracks on the spinning magnetic disks are longer and contain more data than the internal ones. During a rotation, the read-write head may simply write or read more data out than in“, notes from Toshiba.

All categories of hard drives are equipped with history SATA interface, with the exception of high-performance drives available exclusively with a SAS interface. Today the data transfer rate 6 Gbps is a reference standard for the SATA interface and is backwards compatible with 3 and 1.5 Gbps versions.

The SAS standard currently in use is SAS-3.0 and guarantees a data transfer rate of 12 Gbps; It offers higher signal strength, end-to-end data protection, and dual ports but is expensive and has slightly higher power consumption than SATA.

For companies that want to optimize energy costs there are other levers, first of all the modernization of the hard disk infrastructure. Most of the energy is used for disk rotation, storage capacity and workload have minimal influence on consumption; few high capacity hard drives are cheaper than many small HDDs“, conclude Toshiba.

Rainer W. Kaese, Senior Manager, HDD Business Development at Toshiba Electronics Europe, notes that the classifications of hard drives by various manufacturers (PC products, NAS, surveillance, business use) are a good guide. The problem, however, we say, is that until some time ago in the specifications for example, no mention was made of the data storage technology used by each unit. Fortunately, things are changing and if the user is able to understand and weigh the technical datait becomes easier to find and optimally use the best possible hard drive for your needs.


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