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Causation of logical data errors:
Logical data errors
are defined for the purpose of this article, as those
errors that occur in dynamic or static media, which are
either un-related, or only partially related to the
physical condition of the media unit. For this
article, I will define the media unit, as a fixed drive,
removable media [i.e. Zip disk, or floppy disk, tape,
etc.], or as the dynamic memory embedded in a device, to
which power has never been interrupted.
Logical errors can be generated
either by error or malice. Malicious programs such as
public or private viruses can often be the source of
serious logical errors. The program may implement an
agenda of data loss, or data manipulation, which is
contrary to the agenda or objectives of the owners of
the data or media unit. A large number of public viral
programs are well documented on a variety of anti-virus
sites around the world, a couple of note includes
Symantec, and McAfee, but there are also numerous
academic and private sites, which detail the somewhat
predictable actions of public viruses. These programs
are then classified along with private programs with
malicious agendas. Many such programs have be
documented, they are distinguished from public virus by
certain characteristics in that they are often highly
dependent upon a specific system context, and depend
upon privileged logical or physical access to the
system, network, or media unit.
In either case, public or private,
the possible targets of malice are limited to either a
system area, a resource of specific criteria, or a
specific target. A number of system areas are possible
targets. According to the OS, used to format the
drive, [i.e. FAT16, FAT32, NTFS, HPFS, etc.], the system
areas will include a master resource of the media unit.
These master resources may include a bootstrap,
allocation, or organizational resource. If any of these
resources is adulterated with either erroneous or
malicious data, the media unit may be rendered
partially, completely, contextually, or apparently dis-functional.
Examples of such damage are when a DOS based unit
indicated that no valid boot resource is available, or a
MAC fails to initialize.
The adulteration of a key system
area, will often effectively affect the media unit by
the introduction of false program paths, or invalid
resource tables. If false program paths are
introduced, be they well designed or simply erroneous,
will cause the system processor(s) to execute commands
which are either invalid or at the very least not in the
interests of the user. System level programmers are
intimately familiar with such conditions, as execution
paths which lead to data areas, or which cause infinite
loops. When these conditions occur, the results are
highly unpredictable, and possibly injurious to existing
data on the media unit. The possibilities of injury
result primarily from erroneous or malicious commands
that cause good data areas to be overwritten, deleted,
or damaged. The other source of possible functional
damage, which is slightly more common, and preferable to
invalid execution paths, is that of adulterated system
resources. In these instances, the OS or application
damages a key system resource in such a way as to cause
the resource to fail initialization or integrity tests.
This type of damage may also, by containing invalid jump
addresses, cause secondary processes to fail. If for
example the partition table of a media unit is damaged,
then it may appear to have partitions, which are
inconsistent with the actual formatting of the drive.
Symptoms of logical data errors:
Media units with logical data
errors may exhibit a number of characteristic problems,
however the best POST tests are based upon
elimination. If the media unit is recognized by the
system initialization procedure [BIOS], this effectively
rules out many serious hardware errors. Beyond this
test the water gets murky, between hardware and logical
errors.
Many physical hardware errors can
cause data errors, which might also be the result of
logical data errors. Generally the saving grace is that
logical errors are generally fairly systematic in their
expression. For example a disk, which is recognized,
by the BIOS, but reports as having no boot partition is
most likely the result of a logical data error. While
if that same disk was unable to boot, due to file
errors, then the problem is most likely physical.
Specific common manifestations of logical data errors
include missing files, folders, or partitions. Also
when a file contains no data, partial data, or incorrect
data this is most likely a logical data error.
Recovery from logical data errors:
Most logical data errors are
recoverable. If user data has not been overwritten by
the actions of the logical error, it will most likely be
recoverable. The methods to affect the recovery vary
widely according to the source and extent of the errors.
In most cases a senior system
programmer will be able to look at the drive with an
editor, locate important data and move it into another
file. This generally works well if the files are small,
or textual. Larger, or non-textual files, like
graphics or sounds, will require either intact
organizational resources, such as FAT tables, or a
machine language expert will attempt to reconstruct the
file. There are proprietary programs that are used in
the data recovery field that may aid this process, but
they can be extremely damaging in the hands of even
experts who are not intimately familiar with the
delicate data structures, which make up modern media
units. |
