(This article first appeared
in the April 2005 issue of COTS Journal)
Flash SSDs are lightweight, rugged and able to survive high
altitudes and varying temperatures. These characteristics,
plus their ability to achieve faster sustained writes with
no gap between reloads, makes them highly desirable for military
data acquisition and recording.
By Rudy Bruce, BiTMICRO Networks
Data acquisition and recording technology has grown exponentially
over the past years as data recorder manufacturers try to
keep up with faster data gathering speeds and more precise
measurements. Data recording for military and civilian applications
is a major issue, since it could spell the success or failure
of operations or, in worst-case scenarios such as the battlefield,
the life or death of individuals.
One case that comes into mind is the deployment of Spirit
and Opportunity, NASA's twin Mars Exploration Rovers. Equipped
with a variety of spectrometers, cameras and other tools,
their primary mission is to search for answers about the history
of water on Mars. Data recording and transmission is an essential
aspect of this mission, and failure to record/store data would
mean billions of dollars and several years of research down
the drain.
Another concrete example is the flight data recorder (popularly
known as a "black box") installed in civilian and military
aircraft. Implementation of stricter safety requirements for
commercial airlines has led to the development of data recorder
solutions that can gather more parameters with greater accuracy.
More parameters mean less other resources are required to
finish a crash investigation.
Aside from these cases, there are many circumstances in which
data collection and recording is just a one-time opportunity,
making it necessary to deploy reliable data recording equipment
and a storage subsystem that can keep up with input coming
from high-speed sensors. This article discusses the feasibility
of using solid-state flash disks as storage media for these
data recorders, both from performance as well as cost standpoints.
Issues with Legacy Data Recorders
Mass storage has undergone several transformations ever since
the introduction of punch cards during the mid-1800s. The 1940s
saw the introduction of vacuum tubes for storage, while tape
drives began to make their presence felt in the early 1950s.
A couple of years later, magnetic drums were introduced and,
in 1957, IBM rolled out the first rotational hard disk drive
(HDD).
Tape drives and HDDs have survived the onslaught of silicon-based
storage devices and are still available in the market. However,
even though these storage media are widely utilized in business
enterprises, they have weak points that can make them susceptible
to failure under certain data recording applications.
While the magnetic tape drive has been a mainstay in the data
recorder industry, this storage solution has inherent weaknesses:
- Data retrieval is slow due to sequential access: To retrieve
a file, it's necessary to start at the beginning of the
tape and move forward until the file is located. This process
of rotating the tape media back and forth over the drive
head can disrupt the playback of non-sequential data segments.
- Susceptibility to damage: Tapes must be stored in climate-controlled
locations, since they are highly susceptible to damage by
humidity, dust, heat, light and magnetic fields.
- Storage space required: The size of the magnetic tape
is so big that its storage space becomes bulky.
- Quality of recording degrades over time: The quality of
magnetic tapes eventually degrades over time, affecting
recorded data.
Magnetic disk drives, more popularly known as hard disk drives
(HDDs), have solved performance and durability issues associated
with tape drives. However, HDDs are not without their disadvantages.
As files are written onto and deleted from a HDD, data fragmentation
occurs. Fragmentation has a negative impact on performance,
since disk heads require additional time to move around to various
points on the disk to read scattered file parts, resulting in
a gradual deterioration of system performance-longer reads and
extended reboots. In addition, HDDs contain mechanical components
such as the read/write heads and spindle motors which, when
subjected to shock and vibration, may damage the hard disk platters,
resulting in bad sectors.
| Time recorded |
25 hour continuous |
| Number
of parameters |
18
- 1000+ |
| Impact
tolerance |
3400Gs
/ 6.5 ms |
| Fire resistance
|
1100 degC / 30 min |
| Water
pressure resistance |
submerged
20,000 ft |
| Underwater locator beacon |
37.5 KHz; battery has shelf
life of 6 years or more, with 30-day operation capability
upon activation |
Table 1: Flight Data Recorder specifications
Source: NTSB website (http://www.ntsb.gov/aviation/cvr_fdr.htm)
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