# Should I Scan & Fix my external drive?



## calvin-c (May 17, 2006)

I got a new external drive & I'm in the middle of backing up stuff onto it-and suddenly Windows 7 is telling me that there might be a problem & I should 'scan & fix' the drive. I don't want to lose what I've already put on it and I've seen no problems with it so I haven't taken the recommendation yet-should I? It says the problem is likely from unsafely disconnecting it which I never do, but I do sometimes shut down the PC without disconnecting it first-I always thought that went thru the same buffer flushing that safely disconnecting did but maybe not. And then there've been a couple of times when the PC's locked up, forcing a hard boot, but none of those (that I can recall) were while the new drive was connected.

I guess my main question is what 'scan & fix' will do-will it preserve the files I have on it? It's taken a couple of days to get what I've got on there now and some of it is probably my only copy (until I get things sorted out) and I'd rather not take a couple of days to copy things back, then reformat the drive & another couple of days to put them back out there. What triggers this recommendation? As I said there doesn't appear to be any problem with the drive.


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## Ent (Apr 11, 2009)

That message often appears because the drive was not safely removed before being taken out, so the computer makes a point that there could be file system errors. In the majority of cases there aren't, so my instinctive reaction would be to manually run checkdisk against the drive without "automatically fix errors" checked before getting worried about it.

As I understand it "scan and fix" is simply running check disk against the drive. If the file system is indeed corrupted then running checkdisk can make it difficult to recover files by other means, as it puts the file fragments in their own .chk files so recovery software can't see them as anything to be recovered. On the other hand if there is a problem with the file system and you keep adding stuff to it you could worsen the problem. I don't know where the overall verdict would stand, I guess it would depend on how good Check disk's chances of fixing things were, and that's effectively unknown.


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## bbearren (Jul 14, 2006)

I would let Windows "scan and fix", which is basically chkdsk /r. You have very little chance of losing anything recoverable.


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## calvin-c (May 17, 2006)

The problem is that this shouldn't be appearing at all-unless I'm mistaken in my belief that Windows flushes the buffer during shutdown. The drive has never been 'removed' without being disconnected, but I have shut down Windows while it's connected. This should not, unless I'm mistaken, have triggered the error.

Does anybody know what Windows is checking that triggers the error message? I don't see how it could be the entire file system so is it something in the partition table? Or what?


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## bbearren (Jul 14, 2006)

The message appears because the "dirty bit" has been flipped. There are literally dozens of events (if not more) that can cause the "dirty bit" to be flipped, and an improper shutdown/removal of the external drive is only one of them.

The "dirty bit" being set only means that there is a 'possible' file system error. There may well not be any error at all. Let Windows "scan and fix", and then wait to see if it happens again.


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## calvin-c (May 17, 2006)

Thanks. Is the dirty bit set when something starts writing to the drive or when the drive is mounted? Either way the problem (in this case) is that it didn't get reset. Out of curiosity, where's the dirty bit stored, in the partition table?

I did the scan & fix after the earlier response so now I'm just trying to learn more about what caused the 'problem'. Thanks.


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