NTBackup BKS file compressibility

  • Thread starter Thread starter Tom Del Rosso
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Tom Del Rosso

The BKS files don't seem to be compressed, since they are the same size as
the store that was backed up. They aren't compressible either, judging by
my experiment setting the compress attribute of some of them. Do they use
non-compressible encryption?
 
Tom said:
The BKS files don't seem to be compressed, since they are the same size as
the store that was backed up.
Click to expand...

I ran a backup of 100Mb worth of NUL characters to a .BKF file (which is what
Win2K creates; have not tested WinXP); the result consisted of roughly 0x158C
bytes of header (comprising various TAPE, SPAD, SFMB, SSET, VOLB, DIRB, NACL,
CSUM, NTOI, and FILE headers), 100Mb of zeros, then a CSUM and a few other
headers. The file compresses (with gzip) rather well as expected (from 100Mb to
103kb). Checking the 'Only allow Owner and Administrator access' box makes no
noticable difference to the large block of zeros, and consequent compressability.

They aren't compressible either, judging by
my experiment setting the compress attribute of some of them. Do they use
non-compressible encryption?
Click to expand...

What are you backing up? Bear in mind that JPEG, GIF, ZIP, OpenOffice
files(which are ZIP files inside) and a number of other file formats are already
compressed, and any further attempt at compressing them will simply result in
them getting larger instead.
 
Jim Howes said:
What are you backing up? Bear in mind that JPEG, GIF, ZIP, OpenOffice
files(which are ZIP files inside) and a number of other file formats are already
compressed, and any further attempt at compressing them will simply result in
them getting larger instead.
Click to expand...

Thanks for all the data. A lot of my files are already compressed, but I
thought I had enough compressible data files to make that bks file smaller
by more than 2%. I tried a selective backup of the more compressible files
and I see a 45% reduction, so I see that you're quite right.

Since I was trying to determine the benefit of setting the compression
attribute on backup folders, it turns out not to be helpful in any case.
 
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