Massive danger that Hash checksum results are WRONG

[Alan_B]

Windows has a very dangerous short-cut in the memory cache(s).

 

I have just copied a 947 MB file from an HDD to an old and slow 948 MB Flash Drive, and it took 3 minutes to write.

To confirm that the copy was good I then used HashMyFiles from Nirsoft to compute and compare the hash checksums of source and destination files.

 

I was dismayed that the Flash Hash was computed as quickly as the HDD Hash - exactly 17 seconds - because I know Flash don't run that fast,

so therefore Nirsoft was computing what the cache remembered as being written and sent through USB2 connection corruption to the possibly worn out Flash Drive.

 

I Safely Removed the Flash drive to flush bad memories from the cache, and reinserted the Flash,

and then HashMyFiles took a more believable 67 seconds to compute the hash, (which I am pleased to say matched the HDD checksum.)

 

I am horrified at the thought that for years I have validated a file copy without first flushing the caches with a shut-down and reboot.

[Derek891]

I have over a dozen Linux ISO images stored on a 16GB USB stick. Like you, I ran a md5 checksum on every file after I downloaded it to my hard drive and again after it was copied to the USB stick. Every file was a match. But one image remains unbootable, in spite of the fact that I tried four different programs to create a bootable image. I think you may have just explained what is wrong, I'm off to investigate. Thanks Alan, you are a true detective.

[Andavari]

Windows cache is annoying with that, I also unplug my flash drive and then plug it back in so I can get real results.

[Alan_B]

I have now copied the contents of my Sony Flash drive F:\ to HDD W:\#Sony\.

I deleted all files from F:\

I used Portable Teracopy 2.27 to copy from W:\#Sony\ to F:\

After copying all the files Teracopy spent 74 Seconds reading and computing the hash checksums of F:\ and comparing with what had been computed as it read from the source.

 

It would seem that either the cache is NOT updated with the contents of Flash when Teracopy writes to the Flash,

or that somehow TeraCopy is able to access the reality of the contents on Flash instead of the optimistic memory in the cache.

.

I feel a question to TeraCopy support is coming on,

followed by a complaint / suggestion to Nirsoft.

 

Windows cache is annoying with that, I also unplug my flash drive and then plug it back in so I can get real results.

I wish you had told me that before I found out the hard way

[Andavari]

I wish you had told me that before I found out the hard way

 

I found out the hard way myself long ago with video files that were fine on my computer, but my PlayStation 3 complained about them being corrupt.