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"First allocation unit is not valid. Entry will be truncated."


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#1 How Does It Work

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Posted 03 May 2012 - 04:13 PM

Hi,
I'm using an old external hard drive, Western Digital.

I got an error message today when connecting it via USB to my HP Pavilion PC. I've connected it many times and had no trouble accessing the files.

The dialog box said:
Automatically fix file system errors. (This box was checked by default.)
Scan for and attempt recovery of bad sectors. (This box was unchecked by default.)
I clicked okay.
After a few minutes, it said it had fixed errors. I clicked on "View details" and there was a list of at least 30 of my videos shot with my camera that said
"(filename).MOV first allocation unit is not valid. The entry will be truncated."

Can you explain what this means. Is this going to change the playback of my videos? How will the truncation affect them?

All of these videos had been on there for nearly two years and had been watched before and never had a problem in the past.

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#2 James Litten

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Posted 03 May 2012 - 04:48 PM

Hi

It sounds like the drive is formatted with a FAT filesystem. You may be out of luck. It is caused by corruption on the drive that makes the directory table point to the wrong cluster. What I remember off the top of my head is that the first allocation unit is attached to the directory table so if it is messed up all the files in that directory can be affected.

Were the videos all in the same directory?

I have seen this many times with external drives formatted with FAT so I always format them with NTFS whenever possible (sometimes it needs to be FAT like when connecting to an XBox 360). It seems to happen when the drive is disconnected from the computer before it is done with a write operation.

James

Edited by NeverSayDie, 03 May 2012 - 04:50 PM.


#3 James Litten

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Posted 03 May 2012 - 06:03 PM

Okay, I went and verified what I remembered about FAT filesystems since you wanted to understand what that meant but I did not want to just tell you what I remembered because I might be wrong :)

I couldn't find a concise non-technical version buried in piles of low level talk so here's my best shot...

In a FAT file system the directory has a table that contains things like filenames, file sizes, attributes, subdirectories and (most important to this thread) the location of the first cluster of each file.

The computer has the first cluster of where the root directory is hard coded in a specific location so it knows where to start.

Now you have a file in c:\movies\mymovie.mov. The computer finds this by looking at the root directory table and finds the entry for the directory MOVIES and looks at the first cluster value and finds it on the disk and its directory table. The MOVIES directory table has an entry for MYMOVIE.MOV with the first cluster of that file.

Lets say that MYMOVIE.MOV occupies 3 clusters and the directory table says that the first cluster is cluster 6 on the drive. How do you find the other clusters since they are not always next to each other?

I'm oversimplifying some here.
There is a map stored on the drive called a File Allocation Table (FAT) that you can think of as kind of a spreadsheet with a cell representing each cluster that contains a 32 bit number (FAT32). That number represents where the next cluster is or it is FFFFFFFF which means it is the last cluster.
Since you know the first cluster for MYMOVIE.MOV is 6, the computer looks up that cluster on the FAT and in the cell for cluster 6 the value is 7. That means the second cluster for the file is cluster 7 on the partition. When you look at the box for cluster 7 on the FAT it has the value 21 so the third cluster is cluster 21. When you look at the FAT entry for cluster 21 it is FFFFFFFF.

Now the computer knows to get the file by looking at the data stored in cluster 6 then cluster 7 then cluster 21.

So now you see the conundrum of losing the first cluster's value to corruption :( how do you find the other clusters?

You can find pieces in the .chk files but it is very hard to put them back together for anything but text files because of fragmentation.

That's about the easiest way that I can put it.
Hope this helps.

James

#4 James Litten

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Posted 04 May 2012 - 10:21 AM

Need to correct a mistake I made about the .chk files. If those are the only errors that you got from chkdsk, try finding the .chk files it made if you answered yes when it asks if you want to save lost clusters. Change all the extensions from .chk to .mov then see if they play as videos after that.
They are usually in a folder named FOUND.

James

#5 How Does It Work

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Posted 10 May 2012 - 07:02 PM

Thank you James. I appreciate the info and explanation.

How would I check to see if my external hard drive uses FAT? And if it does, would it be preferable for me to change it over to NTFS now that I have data on it?

If I recall correctly, I think the dialog box had said something about being disconnected improperly the prior time. I must have neglected to click the "safely remove hardware" so perhaps that may have caused something to change.

#6 James Litten

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Posted 10 May 2012 - 08:46 PM

Hi

To see if it is FAT, the easiest way is to just right click the drive in Windows Explorer and choose PROPERTIES and you'll see it next to File System:

You can convert it to NTFS but if it were my drive, I would just be careful not to disconnect it without doing the 'Safely Remove Device' option in the systray. From now on choose NTFS whenever you format a new partition for use with Windows (I understand that this is an old drive). If you want to convert it, here are directions...
http://support.microsoft.com/kb/307881

I'm curious, did you find those .chk files in a FOUND folder and did you try renaming them to .mov and see if they are your missing videos?

James

#7 How Does It Work

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Posted 12 May 2012 - 02:13 PM

Thanks for inquiring. Yeah, I don't think I completely understood how to do that. I probably need to find some primer on computer file systems so I can understand the basic concepts first.

This is my understanding so far. A directory is what my PC would label as a folder since I use a graphical interface. I understand the concept of how the parent directories are above the subdirectories, and how the root directory is at the top.

I understand that if a person were to look for a file, they could click on the root directory, then the next subdirectory that would be part of the path, then find the next subdirectory and so on until they found the file.

I don't completely understand what the clusters, cells and allocation units are athough I gather that the system is searching for something that it cannot find because the first part of what it is looking for is missing.

As for finding the files, how do I look for .chk files? I'm not sure entirely what I'm looking for. I've never done a chkdsk before; should I do that when the external drive is plugged in and specify for it to look there?

I'm using Windows 7 64-bit on an HP PC.

Thanks!

#8 James Litten

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Posted 12 May 2012 - 02:57 PM

You've got the gist of it :)

It's very hard to explain without laying down a foundation of concepts that you really never need to know to use a computer.

I'm assuming that your .mov files disappeared after that chkdsk run.

After a few minutes, it said it had fixed errors. I clicked on "View details" and there was a list of at least 30 of my videos shot with my camera that said
"(filename).MOV first allocation unit is not valid. The entry will be truncated."


If so, look on that hard drive for a folder called FOUND and see if it has files in it that end in .chk and change their name so that they end in .mov instead of .chk then double click them and see if they open as the movies you are missing.

James

#9 How Does It Work

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Posted 16 May 2012 - 09:13 PM

Thanks :) Oh, I see what you're saying now. Windows must have automatically run a chkdsk because I did not initiate it.

I attached the drive and did a search for "found" from the Windows Start Menu. I'm not coming up with any folders marked found.

So just to clarify, when the chkdsk said "The entry will be truncated" that means it changed the file from a .MOV to a .CHK ?

Also, one of the other error messages on that list was "The size of the (filename).MOV entry is not valid." This was followed by "The (same filename).MOV entry contains a nonvalid link." The file with this error message was actually there - a little bit had been cut off the end of the file but other than that was intact.

The ones that said they would be truncated are missing. Since I couldn't find the found folder, I did a search for ".chk" This search brought three files that don't look familiar to me:
softokn3.chk Recovered File Fragments xulrunner-windows
nssdbm3.chk Recovered File Fragments xulrunner-windows
freebl3.chk Recovered File Fragments xulrunner-windows

I'm not sure if I should do anything with those...

#10 James Litten

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Posted 16 May 2012 - 10:14 PM

Hi

Do you remember it asking you

Convert lost chains to files (Y/N)?

and if so did you choose yes?

If you chose no then the files probably weren't put in the FOUND folder.

Also, the folder may be called FOUND.000 or some other three digit number.

This was when chkdsk ran...

The dialog box said:
Automatically fix file system errors. (This box was checked by default.)
Scan for and attempt recovery of bad sectors. (This box was unchecked by default.)


James

#11 How Does It Work

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Posted 22 May 2012 - 08:21 AM

No, I don't recall being asked about converting lost chains to files. I had plugged in the external hard drive and right away there was the prompt that there was a problem. I clicked okay with the defaults it had set because I didn't understand what the problem was, and thus didn't want it to infect my computer if there was a serious problem with the external drive. If I'd known I'd had time, I would have asked the question here first before clicking anything.

When checking for this FOUND file or FOUND.000 file, I am clicking on the windows menu icon and typing into the "search programs and files" box. Is there a better way I should be doing this?

Thanks.

#12 James Litten

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Posted 22 May 2012 - 10:57 AM

Hi

You need to look at what folders are on the external drive to see if there is a FOUND.XXX folder of some type.

An easy way is to hold down the Windows key on your keyboard (it has a picture of the Windows logo on it) and tap the letter e one time.
That will open Windows Explorer.
In the left pane select the external drive (it will be in the tree under COMPUTER)
then in the right pane see if there is a folder called something like FOUND or FOUND.000

James

#13 How Does It Work

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Posted 24 May 2012 - 01:30 AM

Thanks. I'll be in the process of looking for a while. I have multiple folders all several layers deep with multiple folders inside of them. Haven't seen anything with the word FOUND in it yet...




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