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Even as a mature, diverse and reliable technology—magnetic spinning disk drives (aka hard disk drives or “HDDs”) continue to grow in capacity, performance and cost benefits. Alternative storage solutions, however, continue to evolve. Hot on the HDD heels—as has been the case for more than 10 years running—are a family of solid-state equivalents.

SSDs (solid-state drives) now sit squarely alongside the other legacy nonvolatile memory solutions, and their presence is being enhanced by interface improvements known generically as non-volatile memory express or NVMe. 

Storage media itself, such as Flash Memory, have seen a multitude of improvements centered on many technological advances. My previous columns have outlined those changes over the past decade. Now we see new steps to improving non-volatile memory solutions, which are in the interfaces themselves.

HDD EVOLUTION

Of the various interface forms for HDDs, those with serial Advanced Technology Attachment (SATA) interfaces

have become the more cost-effective and most prominent of the “everyday application” disk drives. The more expensive serial-attached SCSI (SAS) drives buy the users other capabilities.

When it comes to HDD applications, SAS drives tend to be found more in enterprise computing because of their high speed and high availability, factors crucial for such activities as ATM transactions, stock exchanges and eCommerce. 

Conversely, SATA drives are used primarily in desktops for consumer use and in those less demanding roles such as backups and near-line data storage.

We are omitting Fibre Channel disk drives from this conversation because they are more specialized and less cost effective, but can arguably be justified in high-performance storage applications (such as editing systems) when supported by the appropriate operating and file system technologies.

IOPS AND RELIABILITY

Keep in mind that the best measure for HDD speed is IOPS (inputs/outputs per second), specifically when the drives are in use, under stress and with real applications designed to optimize the drives’ capabilities.

To put IOPS into perspective, industry-accepted averages for 7.2K SATA drives is about 80 IOPS, with the 10K (RPM) devices offering around 120 IOPS and 15K pushing the limits of around 180 IOPS. The equations turn dramatically for solid-state storage devices (SSS), with huge IOPS improvements and no mechanical worries. 

The other factor for SAS v. SATA is reliability. The industry-acknowledged MTBF (Mean Time Between Failure) for SAS HDDs is around 1.2 million hours, compared with 700,000 hours MTBF for SATA drives. This also places SAS clearly into the enterprise space.

Once you move from the HDD world to the SSD world and to other forms of non-volatile memory, the feature sets and interfaces begin to shift. Not only will speed (performance) increase, but the applications for which SSDs can be applied to help increase total system performance—not just from the storage I/O perspective.

Table 1: Some familiar, but less recognized non-volatile memory (NVM) types.

Non-volatile memory (NVM), sometimes called NVS (non-volatile storage), is a classification for a form of digital storage (memory) that retains its state without having power continually applied. Generally, this storage media is without any mechanical components, although that is not necessarily the case.

Optical storage is considered in the NVM classification, as would be any readonly storage that doesn’t require electrical stimulus to retain its state (e.g., a PROM/EPROM). See Table 1 for examples.

Initially, NVS and NVM were intended for secondary storage or for other longterm persistent storage mediums. Today, in its SSD format, it is often used for primary storage to support short-term RAM/DRAM—as in laptops, tablets or mobile devices.

INTERFACE EXPRESS

Besides the physical storage media, electrical and software interfaces are needed to support the “NVM-storage” term. Common interface methodologies include Non-Volatile Memory Express (NVM Express or NVMe) and NVMe over Fabrics (NVMe-oF or NVMeOF). See Fig. 1 for an example of one method for the physical interface.

The “NVMe” term mystifies many, with some feeling these terms are becoming more hype than practicality. We hope to provide some clarification with the following.

NVMe is a host controller interface and storage protocol established to accelerate the data transfer between host/enterprise or client systems and solid-state drives over a computer’s high-speed PCIe (Peripheral Component Interconnect Express) bus. NVM Express (v1.3) is an open collection of standards and information that exposes the benefits of nonvolatile memory (NVM) in computing environments from the mobile device to the data center. The specification, and its registered and trademarked explanations, can be downloaded from the NVM Express Inc. website (www.nvmexpress.org). The term “NVMe” is a trademarked name, which encompasses a solution set designed, from the ground up, to deliver high bandwidth and low-latency storage access for NVM technologies.

The NVMe specification defines a register interface, command set and collection of features for PCIe-based SSDs. Its goals are to enable high performance and interoperability across a broad range of NVM subsystems. Note that, like most “standards,” the NVMe specification does not stipulate the ultimate usage model, i.e., how NVMe is directly associated with a specific solid-state storage, main memory, cache memory or backup memory. 

NVMe is optimized for Enterprise and Client solid state drives, typically attached as a register-level interface to the PCI Express interface. The 287-page specification describes an interface that allows host software to communicate with a nonvolatile memory subsystem. During its development, the specification was referred to as “Enterprise Non-Volatile Memory Host Controller Interface Specification (NVMHCI).” The lengthy name was simplified to NVM Express prior to publication.

Fig. 1: PCIexpress interface card with NVMexpress solid-state drive unit fitted to slot on the interface card. Card uses an M-Key edge socket to attach the SSD to the PCIe form-factor adapter card.

The NVMe 1.3a spec addresses both NVMe over PCIe and NVMe over Fabrics. The later Fabrics specification defines a protocol interface and related extensions to NVMe that enable operation over other interconnects (e.g., Ethernet, InfiniBand, Fibre Channel). Support requirements for features and functionality may differ between NVMe over PCIe and NVMe over Fabrics, rendering different performance parameters based upon the interface application.

NVMe increases support for Enterprise capabilities via enhanced error reporting and virtualization. End-to-end data protection is compatible with SCSI Protection Information, known as “Data Integrity Field” (DIF). DIF (or T10 DIF) is an approach to protect data integrity in computer data storage from data corruption, originally proposed in 2003 by the T10 subcommittee of the International Committee for Information Technology Standards (INCITS). SNIA references this as “Data Integrity Extension” (DIX) in its standards.

KEY FEATURES

The NVMe 1.3a spec interface has many additional key attributes, such as an efficient and streamlined command

set and support for multiple namespaces and namespace sharing. The NVMe Management Interface is the command set and architecture utilized in out-of-band management of NVM Express storage (e.g., discovering, monitoring and updating NVMe devices using a BMC). Typically, the NVM Express controller is associated

with a single PCI function.

In similar fashion to the transitions of HDD interfaces that went through ATA, IDE, SCSI and beyond, now, when you think about solid-state drive technologies, you can add the latest dimensions of the NVMe interface—one of the hotter topics in storage technologies that are growing stronger each day.

Karl Paulsen is CTO at Diversified and a SMPTE Fellow. Read more about storage topics in his book “Moving Media Storage Technologies.” He can be reached at kpaulsen@diversifiedus.com.

Rich Redmond

ALEXANDRIA, VA.—I remember writing a few years about the efficiency advantages of multi-stage depressed-collector IOT tubes used in digital transmitters. At the time, they were state of the art for both power and efficiency, despite their complexity.

Then at NAB Show 2015, it was clear all the transmitter action was in solid-state products, even for high-power UHF applications. Tubes are increasingly hard to find, even for maintenance of older transmitters. This brings up the very real possibility that replacement IOTs may be scarce commodities in five to 10 years.

With the first wave of DTV transmitters reaching the point of increasing maintenance, coupled with possible channel reassignments due to the spectrum re-pack, we wanted to take a harder look at the topic of transmitter efficiency. To learn more, Broadcast Engineering Extra spoke to Rich Redmond.

Redmond serves as chief product officer for GatesAir, responsible for the marketing, product line management and R&D of the company’s transmission products. He is based at the company’s headquarters in Mason, Ohio, outside of Cincinnati.

BE Extra: Solid-state UHF transmitters are now close or equal to the efficiency of IOT transmitters at similar power levels. Is this trend going to continue? Or is there more efficiency to be wrung from MSDC IOTs or some other tube design?

Redmond: As the industry looks for RF systems that are lower maintenance and simpler to operate, the advancements we have seen in high-efficiency, solid-state TV transmitters exemplify that requirement. We believe that is certainly where GatesAir and most transmitter manufacturers are spending research and development efforts, and where supporting manufacturers in power supplies and other RF parts are all investing.

We believe that commercial advancements in MSDC IOT transmitters are unlikely for the foreseeable future. It’s a fairly complex product in a marketplace where the role of the broadcast engineer is evolving, requiring a balance of outstanding IT skills with RF transmission skills. They have as much demand on their ability to have outstanding IT skills balanced with RF wireless TX skills.

BE Extra: What are the key reasons behind the recent improvement in the efficiency of solid-state transmitters? Higher-voltage LDMOS transistors? Better combiners on the amplifiers’ outputs? Something else?

Redmond: Recent developments in high-efficiency solid-state transmitters represent a culmination of many factors. For example, the IT and telco industries really helped to drive advancements in high-efficiency 50-Volt power supplies, reaching an AC-to-DC efficiency of 97 percent. In addition, the wireless base station business has pushed the development of RF device manufacturing to produce higher power and higher efficiency RF devices.

These remarkable efficiency improvements have now been introduced into the DTV world. You take those supporting technologies and combine that with continued innovation on the part of transmitter manufacturers, and the outcome is a high-efficiency transmitter platform like the GatesAir PowerSmart 3D transmitter architecture. In addition, advancements in liquid-cooled transmitter platforms that, in solid-state design, can now evacuate heat from transmitter buildings far more cost-efficiently than in past years, eliminates the need for constant, expensive air conditioning.

BE Extra: If a broadcaster can nurse an existing transmitter along for a couple years, is it likely that efficiency improvement will continue? When does the cost of maintenance exceed the savings (in maintenance and operation) that comes with a new more-efficient transmitter?

Redmond: We’re seeing a lot of broadcasters today who believe the reduced maintenance of solid-state is as important as the power efficiency. The RF engineering base is aging, and few stations want to replace older tube rigs before they understand what ATSC 3.0 and the spectrum repack will bring. But every day you run an older transmitter at lower efficiency, the money spent is not recoverable. The cost of tubes and tube maintenance, the ongoing viability and reliability of tube suppliers, and parts availability compared to 10 years ago make it a risky, and potentially very costly, proposition. Furthermore, switching to a more efficient solid-state transmitter often qualifies for a rebate, so there is potentially an added bonus to the return on investment upon inquiring with your utility company.

BE Extra: Are there any efficiency gains from newer designs for passive RF items, such as mask filters, switches and transmission line? Can tweaking the passive RF components get an extra couple dB at the antenna?

GatesAir 80 kW Maxiva ULXT liquid-cooled, solid-state UHF transmitter

Redmond: There are also some remarkable efficiency gains compared to older power components. We have seen a radical reduction in the footprint of RF output filters, which can now often be hung from the ceiling. For broadcasters who lease space by the square foot in an RF plant, a previously-sized 8-foot wide, 30-foot long RF system that now fits in a 4 x 6-foot space, makes quite a difference in monthly rental costs.

BE Extra: A broadcaster needs a new 35 kW UHF transmitter. What do you recommend: Either solid-state or IOT? Why?

Redmond: We absolutely suggest solid-state over IOT. Solid-state transmitters are significantly simpler to operate, and offer a substantially higher amount of redundancy. In a 35 kW GatesAir Maxiva transmitter, amplification is spread across roughly 40 power amp modules instead of two tubes in an IOT design. Additionally, life expectancy of the solid-state transmitter is easily 15 years at the absolute minimum. If you think about the technical capabilities of your staff 15 years ago versus those of your staff today and project that forward 15 years, the likelihood is that there will be fewer engineers per station comfortable operating liquid-cooled tube transmitters.

Stations and engineers will migrate more to modular components and hot-swappable power supplies that can be easily diagnosed using web browsers and SNMP interfaces. Furthermore, the markedly more compact footprint lowers installation costs, and eliminates beam supplies and building space needs. If I can have a smaller space for my transmitter at my RF site, I am reducing monthly expenditures—especially if I am leasing that space.

BE Extra: There was a recent article that said switching from a UHF channel to a low-band VHF channel would mean the difference between a 25 kW transmitter and a 500 W transmitter to reach the same coverage area. Obviously, there are dramatic propagation differences between the two bands, but the operational savings are significant. Is this something that broadcasters should consider?

Redmond: I would say that the transition from UHF to low-band VHF is something that stations must look at very carefully. There are dramatic propagation differences. You could indeed reduce operating costs quite significantly; however, you must look at the entire delivery chain.

In a low-band VHF operation, the size of the receive antenna on the consumer end needs to be very large to be efficient. Over time, fewer consumers are putting aerials on the roof, and are instead using rabbit ears or integrated antennas inside devices. That consumer behavior makes it more challenging to operate on low-band VHF, in addition to how an increasing amount of man-made noise is rendering VHF frequencies poor for digital TV. That model also makes it more challenging to reach consumers on mobile devices given the needed antenna size. It’s worth noting that there are no DTV deployments globally that use a significant amount of low-band VHF. These deployments are mainly UHF, with some high-band VHF mixed in.