Why Hard Drives Are Here to Stay (For Now)
Storage needs are growing at an incredible rate. Technologies such as mobility, streaming video and the Internet of Things (IoT) are greatly accelerating the amount of data generated, and the possibility exists that we could reach End of Days with regard to storage capacity. Of course, that does not take into account innovation and development of new technologies.
Regardless of what happens with flash or some new category of storage media yet to be imagined, the hard disk drive (HDD) is going to be with us as the main platform for data storage for a long time to come.
“HDDs are and will remain the most effective, low cost, high performance and reliable solution to store the amazing amount of digital data that the world creates,” said Mark Re, CTO at Seagate. “By increasing the areal density capabilities of the drives and by further increasing the number of heads and disks in a drive, we should be able to continue to grow the storage capacity of HDDs in the future.”
Heads are the devices that read and write the data onto the magnetic disk where data is physically stored. The current technology used in HDDs is called Perpendicular Magnetic Recording (PMR). This refers to the orientation of the magnetization on the disks, which is perpendicular to the surface of the disks. This technology was introduced in 2004. The areal density of perpendicular recording continues to increase—although not at the rate it did during the last decade.
As a result, other types of magnetic recording technology have been introduced to continue to grow areal density. Greg Schulz, an analyst at StorageIO Group mentioned several developments aimed at increasing the speed, efficiency and capacity of HDDs. This includes Seagate’s shingled magnetic recording (SMR), which raises disk density in order to gain a 25% jump in capacity. It increases the number of data tracks per inch of disk by squeezing them together so they overlap slightly. The data tracks are actually overlaid, like the shingles on the roof of a house.
Seagate and Western Digital are also working on heat assisted magnetic recording (HAMR) technology. HAMR permits smaller bits to be written by using diode laser integrated onto the magnetic recording head to heat up the disk where data is about to be written. The laser is focused onto the disk using a near-field optical device. The small laser spot (on the order of tens of nanometers) heats the magnetic disk locally to make it easier to switch the magnetization direction, which is how bits are written. When this small spot cools, the data is frozen in place and stable. Reading the data back happens the same way as it is done today.
“Today's perpendicular products have a maximum areal density of a little over 1 terabit per square inch,” said Re. “With HAMR, which should be in products in 2018, we predict the maximum areal density will be around 4 terabits per square inch.”
This could eventually make it possible to store 60TB of data on a 3.5-inch disk. The first such disks are likely to hold around 20 TB and should appear early next year.
Schulz mentioned one further HDD development – helium drives. Helium has only 14% of the density of air. When put in hard drive casings, it reduces the turbulence, vibration and heat generation, thereby lowering power and cooling requirements considerably. Further, you can stack more disks on top of each other inside a drive case, and that means that the data storage capacity of the drive can be increased at a stroke. HGST is already offering helium drives that are said to increase density and lower power consumption by close to 50%.
“Helium-filled drives provide the highest drive capacity possible with more stability and reliability than traditional air-filled drives,” said Barbara Murphy, Vice President of Marketing, Cloud Infrastructure Business Unit at HGST, a Western Digital Company. “Helium-filled HDDs are becoming the leading drive technology for scale-out applications such as active archive and cloud storage.”
HGST's HelioSeal line includes the Ultrastar Ha10, for example, which delivers a 25% capacity improvement compared to drives using PMR. The HGST Ultrastar SN100 is the high-performance version which comes as an expansion card or a 2.5-inch drive.
Further in the future will come Heated Dot Magnetic Recording or Two-Dimensional Magnetic Recording (TDMR). This is a combination of HAMR with physically patterning of the bits, like small islands, on the magnetic disk.
“Heated dot magnetic recording should take us to 10 terabits per square inch,” said Re. “As you can see, magnetic recording has a well-defined roadmap for a long time to come and should continue to deliver the most cost effective, reliable, high capacity data storage products to meet the world's insatiable need for digital data storage.”
That said, he is realistic about the future and understands that it won’t be all disk or all flash. In fact, he even sees a place for tape.
“In storage systems many types of storage will be used, including Solid State Drives (SSD) for hot data, HDD for the majority of the data stored and archive storage, which might be HDDs or tape,” said Re. “A system designer will optimize these various types of storage for cost and performance, but from the number of bytes stored perspective, the vast majority of data stored will be on HDD-based storage.”
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