Dear all,
Thanks a lot for all your kind answers. We will try our best with all the
hints that you suggested.
The approach taking into account the distribution of file sizes and their
slack space seems promising, particularly in a case where the drive to
investigate has been used extensively. I'm wondering, in this kind of
distribution, which percentage of files are system files (thus unlikely to
change over time, even in a heavy loaded system) and wich are regular files.
Well, there is some matter to write "the remains of a long dead file in the
deep slack space" :-)
Take care,
David.
Gary Funck wrote:
I ran some stats on the distribution of file sizes on a Windows NTFS
drive extracted from a computer that had been in use for several
years. Windows XP was installed. There are 44,744 files on the
drive, consuming approximately 18G total.
I put together a quick spreadsheet which calculated the number
of bytes of slack space, given a 4096 file allocation unit.
Here are some results:
0.77% had zero file length (thus 4096 bytes of slack space)
7.37% had a non-zero file length that is an even multiple of 4096
(thus 0 bytes of slack space)
Slack Space
w/ at least N bytes Percentage
32 92.34%
64 92.07%
128 91.50%
256 90.29%
512 86.87%
1024 79.92%
2048 62.91%
2675 49.99%
Thus, if we were to look at the last 256 bytes in each file block
(on this particular collection of files), we'd be looking at roughly
90% of all files on the system, where the majority of the remaining
files didn't have anly slack space at all, and therefore must be
ignored anyway if we're looking to match the last N bytes of
slack space.
The main reason that the figures work out this way is many files
on a typical system are small. On this sample, 44.5% of the files
had a size of 3840 or smaller (at 3840 bytes, there is 256 bytes
of slack space remaining).
--
Responsable des développements informatiques | David.Billard@adm.unige.ch
Division Informatique, Université de Genève | Tel : (+41 22) 379 7977
Battelle Bat A, Rte de Drize 7, CH-1227 Carouge | Fax : (+41 22) 379 7986
