Today’s integrated battlespace includes many tactical systems requiring reliable data storage. Historically, most systems incorporated some type of “moving media” storage device; either with rotating hard disks, optical disks, or magnetic tape. Solid-state data storage systems, based on flash technology, are rapidly becoming the media of choice to replace obsolete magnetic storage in field-deployed equipment and integration into new battlefield designs.
Magnetic media limitations
Most magnetic media and their accompanying drives are not designed to operate within environments imposed by military applications. Adapting media and drives includes creating bulky enclosures with media mounted on springs and other elements that assist in keeping the media and drive environmentally stable and impervious to the basic “shake, rattle, and roll” in military applications. All these extras come at a great cost with the additional space requirements in the computer platform to accommodate the drive plus its awkward enclosure. Add in the additional cooling and power requirements of tape drives and costs continue to mount.
Special enclosures may work adequately with fixed media like rotating disks, but they represent yet additional challenges for removable media like tape drives; to remove the media, the enclosure integrity must be compromised. When the media is removed, it must be protected from contamination or exposure to unfriendly environmental conditions. Removable flash technology provides a reliable solution to address these concerns.
Defense applications ranging from unmanned aerial vehicles to missile ground communications have used tape media with mechanical drives to record data. Flash technology presents significant advantages over tape. Flash media storage systems, both removable and fixed, contain no moving parts and are capable of operating in the harshest of environments, offering extreme reliability and durability. In most applications, there is no need for special enclosures.
Comparing tape and flash
There are many tape-drive variations on the market today - some for data backup and restore functions. Many tape drives in embedded military applications are designed as desktop drives. The comparison between desktop tape drives and flash storage narrows down to five main categories: environmental considerations, performance, reliability, security and life cycle management.
Flash drives, which contain no moving parts and are capable of operating in the harshest environments, benefit from:
• superior durability for shock, vibration, temperature, humidity, and altitude;
• relatively low power consumption and low heat generation, which is important in embedded applications; and
• lack of acoustic signature in flash, which is critical where detection could result in loss of life or positional information.
Flash drives have many undeniable and significant environmental advantages over its aging magnetic-tape counterparts.
Performance
Never has performance been more important than in the contemporary battle theaters. Each service branch potentially communicates with other branches on missions through high-speed interfaces and over significant distances, which puts an even greater burden on data-storage performance.
To compensate for slow performance, tape-drive manufacturers use data buffers as large as eight to ten megabytes in contemporary products. Buffers present a source of data loss when the tape drive loses power. Between the high buffers and data compression, tape-drive performance numbers improve, but at the potential sacrifice of data integrity. Flash drives that are designed without cache (analogous to tape buffers) provide relatively high data reliability during power outages without sacrificing sustained read and write rates.
Tape-drive performance cannot compare to flash drives because of mechanical constraints. Contemporary tape drives have made significant advancements in the speed of positioning the tape heads while searching for tape marks. Average access times range from 20 to 60 seconds depending on tape length and mechanics, and tape load-to-ready ranges from 10 to 30 seconds. With fixed flash drives, tape head positioning and load-to-ready do not slow performance. Access to data is nearly instantaneous. By virtue of emulating certain tape functions, such as rewind-to-end and search-to-end, there is no delay on a flash drive.
Reliability
Mechanical devices, such as tape drives, are vulnerable to the elements. Our most recent battle theater in Iraq is no exception. The desert with its extreme temperatures, nondescript geography, wind, and sand has proven to be one of the harshest environments on Earth. While temperature and geography are serious issues, the most difficult aspect of this environment is the sand. Most often reported to having the consistency of talcum powder, sand remains a constant threat to personnel and all devices with moving parts.
When evaluating storage reliability, mean time between failures (MTBF) is typically scrutinized. There are many ways to calculate MTBF. MIL-HDBK-217F is most frequently used in the military but there are other standards such as Telcordia SR-332 (formerly Bellcore) and the Six Sigma approach based on actual failure rates over a period of time.
Within standards, variations exist based on the characteristics of the components, the environmental conditions, and other factors. Even among flash vendors there are huge variations in MTBF calculations. An “apples-to-apples” comparison is achievable only by asking the vendor which method he used, how he derived his calculations, and under what environmental conditions.
Most tape manufacturers today quote tape drive MTBF up to 300,000 hours at a 100 percent duty cycle, which is defined as power on hours (POH) by most tape- drive manufacturers. Most tape manufacturers are clear that the quoted MTBF can only be achieved if maintenance is performed on the tape heads in the form regular cleaning and replacement every 30,000 to 50,000 tape-contact hours. Integration of flash devices into these systems eliminates preventive maintenance and its associated downtime. Enhanced system reliability and increase operational readiness are the results.
Security
The need for data-storage security was driven home when a Navy EP-3 surveillance plane collided with a Chinese jet fighter in April 2001 and was forced to land in hostile territory. Disk drives were physically destroyed with hammers to prevent valuable data from being compromised and lost. While this may work for rotating disk, it is much more difficult to physically destroy hundreds of feet of tape with a hammer. Magnetic degaussers are bulky and costly and may not be practical for field-deployed military applications.
A typical flash drive available on the market today offers several levels of secure erase functionality compliant with the NSA and various Department of Defense specifications. A clear operation is a simple sector-by-sector erase with verify. The flash drive is usable after a clear option. A sanitize operation is a sector-by-sector erase with verify and a pattern overwrite to eliminate traces of the original data. A destroy operation completely destroys flash memory, rendering the flash drive completely secure. The time it takes to perform these various operations depends on drive capacity.
Life-cycle management
The useful life expectancy of military equipment varies somewhat but generally remains in the field for 10 to 25 years. There is the probability that a piece of equipment may undergo an upgrade within that time period but replacement parts and spares should be available during the useful tenure of the device.
Some tape drives have been in use for many years and have reached their maturity stage. As these drives become obsolete, engineers face costly redesigns, re-qualifications, and documentation changes that have the high probability of recurring again in a short time period as removable storage manufacturers redesign or obsolete the current product offerings.
Flash tape drives can be tailored to emulate virtually any current tape drive command and option set, thus reducing or eliminating any programming or design changes in existing systems. As additional components within the system are replaced or upgraded; if necessary the flash tape drive can again be updated to match the requirements of new system components. Given this flexibility, project times required to integrate, update, qualify and deploy are significantly reduced. This same flexibility extends to subsystems within the supply chain by allowing them to be updated; preventing obsolescence, protecting investments and maintaining the required level of operational readiness.Al Schwartzis a field application engineer at Adtron Corp. in Phoenix.
