Hard drive at 100 km / hour for reading data

A hard drive is much more than just storing data, files, photos of your wedding, graduation, personal documents, or to install applications and use as a cache of information for temporary data.

A complex system, designed to always have maximum performance to keep data safe for as long as possible.

Find out now about some differences about GMR, TMR, PMR and SMR, and what they really are.

When you view today's 16 TB data hard drives, you only see the acronym SMR, but what is it really?

Hard disks are built with a magnetic material, this in turn is a plate with thousands of grains of ferrites that are there ready to determine the domains, and these domains will form part of a larger magnetic structure, where it is represented by the information of fact.

Below, what the ferrite grains look like and how they are arranged on the hard drive. Notice, there is nothing ordered as you can imagine:

50 nm display scale

100 nm display scale

The images were made by Yale University, using magnetic microscopes, since this area is so small.

10 nm scale, grains within a domain. The "stripes" are the atomic layers of the atoms that make up the ferrite. At such low zoom levels, atoms are not that small.

But in addition to having the media, ferrite grains, and domains (which is nothing more than a group of grains to compose information, since a grain alone is too weak to activate the sensors), then we have the sensors.

The AMR, GMR and TMR sensors are not only sensors used in hard drives, but also for many other applications in different types of applications, even for automated car parking on the streets.

These sensors work with a magnetic signal reading level, being able to read their levels, and thus pass it on to a controller to determine and understand its signals.

The discs are usually known for using the TMR, PMR or SMR sensor, and in some materials, the TMR can also be called CMR, or "common magnetic recording". They change with each term, the engineering adopted for reading and writing.

Hard drives with at least 250 GB of space, up to about 1 TB, are generally noted as PMR, which is perpendicular magnetic recording, leaving many ferrites standing on the disk, increasing the space for the domains , in front of the TMR discs.

Beginning with 1 TB disks, new size limitations began, and companies began to further reduce domains using SMR technology, "shingled magnetic recording", and then it was possible to adopt 10 TB disks, 12 TB and so far, 16 TB commercially by Seagate.

There is a problem, however, with SMR disks: The data is in such small domains that it can overlap with each other, that is, whenever new information is saved, it is still recorded using PMR technology, but as soon as the data they are combined, they are rewritten in dense areas, since the reading and writing arm is larger than the domains, and then they are read and written in a combined way.

To the detriment of performance, SMR-type disks need idle time to perform data sorting, and rewrite, unlike PMR disks, which do not need to do any work right after the data is saved.

An SMR-type disk if it is constantly accessed for reading / writing and does not have enough time to be idle to start its work of reorganizing the data, can suffer from frozen areas, where only reading actions are allowed, with a degradation in the performance of read / write.

This data reorganization scheme is also present in most SSD drives on the market today, with the advantage that they can do this job quickly, usually in time of use.

For this reason, the use of SMR and PMR disks in RAID arrays is not recommended, as SMR disks can degrade the performance of other disks that do not need sector reorganization actions.

And, for curiosity, regarding the title, yes, a simple disk of 5400 RPM, according to Yale University, makes the reading arm at 100 km / hour, or 62 miles per hour to read the domains and recorded information. on the hard drive tracks.

References:
Hard Disk Methods and Materials, Yale University, https://volga.eng.yale.edu/teaching-resources/hard-drives/methods-and-materials.

What's the Difference Between TMR and GMR sensor? - Eletronic Design, https://www.electronicdesign.com/industrial-automation/what-s-difference-between-tmr-and-gmr-sensors.