Corruption when copying files from GPT via USB2 to external MBR

I use Macrium for partition images and whole disc image backups which go via USB to my external HDD.
Never failed with my 7 year old 32 bit XP Laptop and Comodo 3.14.

I now have a much more recent high powered 64 bit Desktop with a clean install of Windows 7 Ultimate, using Comodo 5.3.176757.1236.

A Macrium Boot CD created on the external drive a 6 GB image of the Desktop primary MBR HDD,
and this validated perfectly.
Because it was a Boot CD there could be no corruption by Comodo.

Macrium has created on the secondary internal GPT drive 4 off 6 GB images plus 4 off 1 GB Differential images, all perfectly validated.
For extra security I selected all 8 images and duplicated this group on the external drive, using the normal Windows drag/drop copy procedure.
The smaller differential images were lucky, their duplicates validated.
Only 1 of the 6 GB images was lucky, the other 3 failed to validate.
MD5 checksums confirmed the 3 failures were different from the originals,
and repeating the checksums got the same consistent answers - errors on what had been written.

My experience with Comodo 3.14 was that when copying or scanning a larger group of files,
everything was much faster and smother if I disabled A.V. and Defense+ (and of course blocked the Internet).
Therefore I set Comodo 5.3 to block the internet and disable A.V. and Defense+,
and then I successfully duplicated the images which were validated.

Comodo Active - 3 failures out of 4 attempts
Comodo Passive - 3 successes out of 3 attempts.

Those statistics indicate a fair chance that Comodo is implicated in a data corruption of 1 bit in 6,0000,000,000 * 8
either because Comodo did damage, or because it was consuming precious processor cycles with concerns about the safety of the files that Windows was copying,
or perhaps Defense+ has never seen a file being copied from a GPT dynamic disc via USB2 onto an external MBR disc.

I suspect that Comodo may not ignore the 6 GB files, but detect that they contain millions of compressed files,
hence lots of inspection.

Should I tell the A.V. to ignore the Macrium image file extension which is “MRIMG” ?
By default the A.V. has “exclusions” which include “C:\Program Files\COMODO\COMODO Internet Security*”
Can I add to the list “*.MRIMG”
Or do I have to also stipulate the Drive and Path of the original and or the intended duplicate ?

Is there some adjustment to Defense+ that would reduce its concerns about copying from GPT to MBR ?

Any advice will be appreciated.

N.B. For many years I was happy with FAT32,
and regret my loss of control under NTFS where permissions always strike at the worst possibles times.
I know very little about GPT and that make me nervous ! !


What happens if you copy from one mbr disk to another mbr disk? Does the same thing happen or not? That way we can determine whether the problem is related to GPT dynamic disks or not.

The errors only happen when I am not looking ! !

Transferring 1.5 GB has always been lucky - so far
It seems to require the transfer of 6 GB to be unlucky,

When I first saw the problem I was simply using Macrium to validate the 6 GB duplicated image on the USB2 connected MBR,
and Macrium aborted early at about 10% of the way through the 6 GB file when a checksum misfired.
This demonstrates that after transferring 0.6 GB an error occurred,
so I deduce that had End Of File occurred at 0.7 GB the image would still be invalid.
(n.b. I believe Acronis uses fewer checksums per MByte, but the worse thing is it never said WHERE the error occurred.)

I think I need to observe how many errors occur when duplicating 60 GB of files so I may be 90% confident of the probability of success with a 6 GB file

Individually selecting and copying 6 GB files via Windows Explorer and then individually validating each is a pain.
I cannot face doing this for 10 files.
I have now installed TeraCopy which will accept one set of many files,
and I can relax whilst it copies and validates each file and concludes with a success/failure report.

I propose to use TeraCopy to duplicate a total of 60 GB :-
From GPT to Internal MBR C:\FirstSet
From C:\FirstSet to C:\SecondSet
From C:\SecondSet to External MBR
I may be gone a while ! !

Please advise me if there is anything further I should test.