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#26861 - 09/26/13 08:00 AM USB flash drive
jaybass Offline


Registered: 08/04/09
Loc: toronto Canada
OS 10.6.8 Is there a way of detecting a glitch in a flash drive that has downloaded a program? I ask because this particular program froze about 75% through the playback. I had to restart from the beginning and fast forward to a point just past where it froze and then it played on to the end. This has happened twice on the same consecutive TV program downloads. I use a Kingston 64 GB USB flash drive on a sony player. jaybass

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#26862 - 09/26/13 10:46 AM Re: USB flash drive [Re: jaybass]
joemikeb Offline
Moderator

Registered: 08/04/09
Loc: Fort Worth, Texas
Disk Utility, and Drive Genius can check the volume structure of a Flash Drive, but that does not validate the contents of the files on the volume. TechTool Pro will validate files, but TTP 7 does not even "see" a flash drive mounted on the Mac. If yo know or can obtain the checksum of the suspect file MD5 can calculate and verify the checksum.
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#26869 - 09/26/13 01:08 PM Re: USB flash drive [Re: joemikeb]
jaybass Offline


Registered: 08/04/09
Loc: toronto Canada
joe, thanks for your reply.
a93d4b5595ff46d31a8d8944db0610c7 and c253481c5a1f24837edfa4c26bfcf3e9 The first one is MP4 ad the second one is DivX. I converted the MP4 to DivX but I don't know what those numbers mean... or do I need to know? The error did not occur in the DivX playback. Why I have no idea. I used iskysoft to convert. I am not conversant with 'checksum'. I'll google it and see if I can understand it. I have TTP6, is that version of any use? jaybass

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#26874 - 09/26/13 02:59 PM Re: USB flash drive [Re: jaybass]
joemikeb Offline
Moderator

Registered: 08/04/09
Loc: Fort Worth, Texas
For a checksum to be of any value you would have to have the checksum for the original undamaged file and compare it to the checksum created from the copy you have.

Try a new download if that is possible
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#26889 - 09/27/13 06:55 AM Re: USB flash drive [Re: jaybass]
Virtual1 Offline


Registered: 08/04/09
Loc: Iowa
could also be a sign of bad RAM in your computer.

Of all the OS installs I've done throughout the years, of the ones that failed (5%? yes really that many) maybe 1/8 of those were due to an error reported with the media. 80% of THOSE were actually due to bad ram. What happens is the package is decompressed, and then the entire package is checksummed against the stored checksum in the package. If they don't match, it usually reports an error that looks like a bad DVD. But that error is actually indicating bad RAM. (the data while it lived in memory during the decompress got corrupted, and written to disk badly, then failed the checksum later)

Also "detecting a glitch in a flash drive that has downloaded a program?" - as in, you are downloading directly to a usb flash drive? or are you talking about an SSD? Or a Flash player (web browser) download?

A few groups of things publish checksums. When you go to an apple software update download page, it lists the MD5 checksum iirc. And almost all unix repos list the CRC or MD5 or SHA1 of the packages. (geeky users like that have no problem with checksumming packages)

cat (drop flie from Finder into terminal window now) | openssl md5

example in terminal:

apple:~ virtual1 $ cat /Users/virtual1/Desktop/for_mom.jpg | openssl md5

displays:

8a78a24424ccc8372991951bcfcd978a

That is the MD5 checksum of the file. Openssl will only checksum the data fork, and only of a single file. You can use that to verify if a file has been damaged, altered, or truncated by comparing this number on the sending and receiving end. there are other options besides md5. Bizarrely enough, CRC32 is not one of them.
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#26900 - 09/27/13 08:23 AM Re: USB flash drive [Re: Virtual1]
jaybass Offline


Registered: 08/04/09
Loc: toronto Canada
Great stuff Virtual1, I wish I understood everything you said. If I did, I wouldn't have asked for help. I download from torrent search engine and then from kickasstorrent directly to my HD. I download about a dozen TV episodes/movies a week without any problems except for the odd fake. I have 8Gb Kingston ram which I renewed a few months ago which I'm sure is okay considering all the downloads I've done. Yesterday I downloaded the TV episode that followed the 2 episodes that froze and it played just fine. Maybe it's something that's inexplicable. However, since DivX copies are not corrupted, I'm satisfied.
Thank you for your comprehensive reply. jaybass

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