HDDs Are Still Spinning (Rust Never Sleeps)

Monday Oct 21st 2013 by Greg Schulz

Contrary to some accounts, traditional spinning disks continue to play a major role in enterprise storage.

Given that 2016 is coming up rapidly upon us, it’s likely that the HDD will see its 60th and perhaps even 70th birthday given recent and upcoming enhancements.

The Hard Disk Drive (HDD), despite being declared dead for decades, is still very much alive in traditional, virtual and cloud environments. What has occurred over several decades is a consolidation of HDD manufactures from dozens to three (Seagate, Toshiba and Western Digital (WD), something similar to what is occurring with the nand flash Solid State Devices (SSD) market.

Performance, more than RPMs Traditionally, Revolutions Per Minute (RPM) were an indicator of HDD storage performance in terms of IOPs, seek, response time, as well as helping to contribute to spiral transfer rate (bandwidth). RPMs still play a key role in storage performance with HDDs, but some of the old rules of thumb about number of IOPs and other metrics may not matter as much if they are dated.

Some will see it making intuitive sense: the smaller 2.5” 15K HDDs being faster than their 3.5” counterparts. However, there are also other improvements such as cache and buffering, using more DRAM as well as Non Volatile Cache (NVC), not to mention nand flash SSD with Solid State Hybrid Drives (SSHD) or Hybrid Hard Disk Drives (HHDD).

Then there are the performance optimizing algorithms, improvement in internal processing performance capabilities that help combine to boost performance. What is not as intuitive is how a 2.5” 10K RPM HDD can be faster than a previous generation 3.5” 15K SAS HDD.

Sure, there is the usual assumption the performance boost comes from going from 3Gbs to 6Gbs SAS, however there is more to it than that. Likewise, a 5.4K or even 5.9K drive can have the performance of a traditional 7.2K.

More to HDD performance than just RPM

While not a direct analogy, think of it this way: If you have a vehicle and look at your engine’s RPM gauge and speedometer, just because the RPMs increase at some point, a different gear is still needed to become more efficient and effective.

For example, shift out of a lower gear into a higher or highway gear, and that results in the RPMs going down a bit, yet speed increases.

While HDDs do not have discrete gears per se, or at least that are visible or noticeable, there are other things that help boost it into a turbo mode, so to speak. In addition, HDDs from desktop to enterprise class to high performance to capacity optimized are also seeing more DRAM-based cache buffers, which can range from a few 8MB up to 128MB on some devices. This cache is used for general buffering as well as assisting with read-ahead and other optimizations.

SSHD and HDD turbo modes

If you need even more performance, or want to stop short stroking 15K RPM drives and their resulting under-utilized storage space capacity, then take a look at the Solid State Hybrid Drives (SSHD) such as the Seagate Enterprise Turbo 600GB 2.5” SSHD.

Unlike the previous generation Hybrid Hard Disk Drives (HHDDs) that I have been using for a couple of years for some applications that were only read optimized, SSHD also accelerate writes.

The amount and type of nand flash varies from a few GB to 32GB on some models, along with mix of SLC, MLC and eMLC. Granted, these SSHDs are not as fast as an actual SSD, however at a given capacity and price/performance point they fill the gap between traditional HDD and SSD. Sure, the workloads will make a difference, but if, for example, you are using HDDs and short-stroking them for read and write performance because you cannot afford SSDs (that is a different discussion), then you should be looking at SSHDs.

Rust never sleeps and energy effectiveness

A popular expression refers to HDDs as “spinning rust,” given that they are magnetic recording devices and hence linked to oxide (e.g. rust).

Except for spin-down drives, many HDDs today support more advanced intelligent power management (IPM) aka Green or Energy Efficient features. Various vendors have different specific names for the IPM feature functionality across their diverse drive line-ups. IPM is a generic term that refers to a collection of functionality from varying drives RPM, slowing down or disabling electronic circuits when not needed, to overall more effective power management.

In other words, IPM aligns the right energy effectiveness option to meet different demands without compromising on performance, availability, capacity or economics. For example instead of prior generation HDDs that consumed 15-18 or more watts of energy while in use (excluding startup-up surge), current generations can be as low as a couple of watts (or less) or around 8 watts on the high-end when being used.

Speaking of old rusty FUD pertaining to HDDs, from an application, operating system, file system, hypervisors or even storage controller standpoint, data is accessed using Logical Block Addressing (LBA) and Logical Block Number (LBN) or virtual addressing if you prefer. These virtual addresses mask the underlying cylinder head sector (CHS) access used several decades ago. Unfortunately, some believe or spread the rusty FED that HDDs are still accessed via CHS. Perhaps it is time for some old FUD to be declared dead?

Sizing up HDDs

The areal density (amount of data that can be stored in a given amount of physical space) continues to increase. This means we will see even higher capacity HDDs beyond simply stacking more platters (surface area for storing data). HDDs today come in various form-factor sizes with higher capacities (e.g. 2TB, 3TB, 4TB and soon larger) being 3.5” of various heights using primarily 6g SAS and SATA with some 3g SAS, SATA and 4GFC (Fibre Channel) devices still in the market (both desktop and enterprise classes).

The 2.5” form-factor size for both mobile/desktop and enterprise class drives across performance and capacity is where many things are happening. This includes ultra-thin 5mm devices for tablets, or 7mm for laptops and ultra-books, to 9mm high 1TB drives spinning from 5.4K to 7.2K.

Remember what was mentioned above that there is more to performance today than just the RPM speed. For higher performance there are 7.2K, 10K and 15K along with Turbo SSHD 2.5” drives supporting 6g SAS and SATA with 12g SAS devices starting to appear.

More to HDDs than size, capacity, power and performance

The software for feature functionality of HDDs continues to be enhanced, as does the ease of which it is to apply new firmware for maintenance or fixes. Features that are available on drives besides performance optimization, improved availability, and energy or power management include Self Encrypting Devices (SED).

There are various types of SEDs, including those that support FIPS 140 and TCG Opal specs. One of the benefits of SEDs is the ability to do fast drive erase, shortening the amount of time needed when safely disposing of HDDs.

The benefit is that the device can be used longer for actual work vs. being off-line. Other features include vibration and noise dampening for high-density configurations, and Advanced Format (AF), supporting 4Kbyte blocks vs. traditional 512 byte. Manufacturers’ warranties on HDDs also vary from two to five years for different drives that will also differ based on the system or solution provider and what they choose to offer you.

HDD tomorrow and today

HDDs are seeing improvements in space capacity due to continued improvements with areal density, also with new enhancements such as Shingled Magnetic Recording (SMR) and – coming soon – Heat Assisted Magnetic Recording (HAMR).

SMR-based drives are starting to appear in the market and are a good fit for write seldom, read often types of environments such as archive, reference or static data, given their capacity increase. The capacity increase over the same base drive comes from placing data closer together, in a pattern that resembles the shingles on a roof while maintain data integrity.

Also watch for Ethernet-based drives to appear. Granted they may not be for iSCSI or NAS (at least on a native basis). These and other improvements will continue to push out or delay hitting the preverbal brick wall or the point where the super parametric barrier prevents HDDs from being enhanced further. For what it’s worth, we were supposed to have hit the super parametric barrier several times over the past couple of decades.

Happy 60 birthdays in advance to the HDD, which continues to be used in traditional, virtual and cloud environments from enterprise to desktop and mobile.

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