Story of this program.
The covert threat.
As well as many other PC users, I from time to time copy the files which
have collected at my hard disk to compact discs. And as CD-writing drive at
our office only one, I am due to copy these files over a local area network
to the computer with this drive.
Having done once again this operation, I have found out, that the ZIP-file
written down on a compact disc can not be unpacked. It has slightly surprise
for me, since neither at copying, nor at recording, at the subsequent reading
I did not receive any error messages. More detailed investigation has revealed,
that the file was damaged at copying over network. Fortunately, I had not time
to remove an initial file, and simply anew have copied a file.
After that case I have decided, that it is necessary to find means for the
control of integrity of copied files. After short searches I have found the
md5sum utility. This utility calculates the checksum of the
specified files by MD5 algorithm. By comparing the checksums of a file before
and after copying, I can check up identity of an initial file and a copy.
It was all that is necessary for me!
Having begun to use this utility I have found out, that each time when
I copy files to CD - R, usually several files has been found damaged. These
damages occurs both at a stage of copying over a network, and at recording
on CD - R. I do not know, why it occurs: because of bad quality of the
equipment, or because of the software bugs. Or, maybe, the error correction
algorithms incorporated in them begin to give failures at such volumes of the
information. At least, now I had means of detection of the latent damages and
I was once again convinced, that extra check never will superfluous…
Alternative.
Thus, this small utility has helped me to avoid possible losses of my data.
Only, he had one restriction: can't process subfolders. To process a tree of
folders I move in subfolder, launch the md5sum, move in the following subfolder,
etc… It was rather tiresome and took away from me a heap of time.
I have decided that this process should be automated. Of course, to make
recursive detour of subdirectories in language of scripts in Unix, this utility
whence has come, it would be simple enough. Moreover, the version of the
utility under Unix already had a feature for work with subdirectories.
However, I needed such means under Windows and I still wanted to make some
additions for the even greater automation and convenience of use.
In result I have written the program and called it Advanced CheckSum
Verifier (in further ACSV). The program has two modes of operation: updating
and verifying. In the updating mode it create special files with the checksums
of files in the specified folder. In the verifying mode the program read these
files and compares these values to the current checksum values of files. And if
it finds out discrepancy (or absence of any file) the error event will be
logged.
Now I launch the program, it start to scan the specified folders tree, and
I quietly am engaged in the affairs. After completion of scanning, I look
through the processing log. If I find files which has been damaged, I leave
them for the next session of recording to CD - R. And speed of work of the
program high enough: on my PII-400 under Windows NT 4.0 with 50-speed ASUS
CD-ROM, the checking of the whole compact disc occupies about 2-3 minutes.
Earlier when I used the program md5sum, it took away from me almost half an
hour (if there were many folders).
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