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What does "quick format" and chkdsk NOT do?!

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December 28, 2012 6:57:38 AM

I have two external USB2 HDDs which I have had for years without problems but last week someone managed to damage them both in a way that the files seem to be there but when I look at the files in detail, there are errors. I'm not asking about the reason for the damage (I think most probably it is since he kept pulling their USB connectors in & out often and since devices with ungrounded AC/DC adapters often have >100VAC when you measure benween ground on HDD and PC before connecting them, you really rely on hot swapping to be properly implemented by connecting GND before the other pins, but it could also be due to heat or ESD).

Anyway, I copied the files to the external drives again, but they still had errors. So I ran CHKDSK /F but it still had errors after that and CHKDSK reported no errors (like bad sectors). So I made a quick format and tried again but same errors. Finally I ran a format from the CMD windows without the /Q option i e NOT a "quick format", waited for 3 hours, no errors were reported by FORMAT. And after that I could copy my files to the external HDD without errors. For both my drives.

So the question is: What does "slow format" do compared to "quick format" that can explain that it manages to repair my drives? (I know "slow format" is not a full "low level format" and that it looks for bad sectors and would add a boot sector if these were bootable drives, but I though quick format + CHKDSK /F would do the same as a slow format.)

I found other threads on diff between qucik format and slow format but none that explain this. Also found this thread from Microsoft regarding XP which isn't very detailed: http://support.microsoft.com/kb/302686/en-us

More about : quick format chkdsk

a b G Storage
December 28, 2012 7:43:02 AM

Basically quick format just wipes the file table and leaves the rest alone. A full format goes sector by sector, and when a bad sector is found, it reassigns it so it will not be used. Of course the more sectors the longer this takes (hence the bigger modern drives get the most time it takes and the less likely a full format will be performed). Checkdsk is sorta of in-betwenn, and doesn't all the permissions that format has. It checks the validity of files and file allocation table, and tries to fix where it can (w/f of couse), part of which is finding straded files or entries. It is designed to be quick, and doesn't do the "free" space checking and reallocation that a full format would. A full format may result in a decreased drive capacity, chkdsk will not.
December 28, 2012 8:19:31 AM

But wouldn't CHKDSK and "slow format" report if there were any bad sectors? Cause they didn't.

Does "slow format" perhaps also do some formatting that "quick format" doesn't, that can be useful for a damaged drive? (Besides checking bad sectors.)

Than ks for the reply BTW and happy holidays!
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December 28, 2012 8:47:46 AM

But wouldn't CHKDSK and "slow format" report if there were any bad sectors? Cause they didn't.

Does "slow format" perhaps also do some formatting that "quick format" doesn't, that can be useful for a damaged drive? (Besides checking bad sectors.)

And I just checked reported "capacity" for these two 300GB disks, and one is 320 070 479 872 and the other 320 070 287 360. I would have guessed all "300GB disks" are the same number of bytes so this might indicate missing sectors? Or perhaps it could be due to them having different hardware (number of sectors/cylinders/heads/platters)? Is there no simple way to get a report on number of sectors marked as "bad"?

Thanks for the reply BTW and happy holidays!

(PS Getting annoyed with this forum's editor now as well.. Tried to edit my previous message and when I pressed "post it" it said "not allowed to edit" and my whole text was gone.. and links and formatting doedn't work for me.)
a b G Storage
December 28, 2012 9:10:31 AM

Quote:
"But wouldn't CHKDSK and "slow format" report if there were any bad sectors? Cause they didn't."


There is also scandisk, but both of these are older and basically discontinued. CHKDSK doesn't look for bad sectors as much the results of bad sectors, but these days logs are confined to DOS. Format will, but doesn't always report them unless in a DOS, and scandisk will, again in DOS. Blame MAC's for newest Windows OS trying to "simplify" things for users. Too complicated right? Yeah, sure.

Quote:
"Does "slow format" perhaps also do some formatting that "quick format" doesn't, that can be useful for a damaged drive? (Besides checking bad sectors.)"


Yes, but few people want to wait overnight, and as far as a new disk, a quick format is generally sufficient. The time for a full format is directed tied to the size of the drive. So a 100MB drive isn't so bad, but a 100GB drive is a pain, and 4 TB drive, well, you get the point. Once upon a time a full format was the suggested way for power users, but eventually even they/we switched to quick.

Quote:
"And I just checked reported "capacity" for these two 300GB disks, and one is 320 070 479 872 and the other 320 070 287 360. I would have guessed all "300GB disks" are the same number of bytes so this might indicate missing sectors? Or perhaps it could be due to them having different hardware (number of sectors/cylinders/heads/platters)? Is there no simple way to get a report on number of sectors marked as "bad"?"


Some variation is quite common and to be expected these days, there is some variation due to marketing and some is due to legitimite size measure disputes, almost like metric vs english. Is a GB 1 billion bytes, or 10 billion bits, or a binary power of 2? And again, DOS will report the number of bad sectors.

Quote:
"Thanks for the reply BTW and happy holidays!"


You're welcome, Merry Christmas and Happy New Years!

Quote:
(PS Getting annoyed with this forum's editor now as well.. Tried to edit my previous message and when I pressed "post it" it said "not allowed to edit" and my whole text was gone.. and links and formatting doedn't work for me.)


P.S. We all have similar complaints. They are in a beta redesign of the forums, we'll see if it's better or worse.
December 28, 2012 7:04:49 PM

Thanks for the reply.

By "DOS" do you mean "CMD window (in Windows 7)" or do you actually mean I should dig up my old DOS diskettes?

I don't have scandisk as a command in the CMD window. And I did run format in a CMD window but it said nothing about bad sectors.

I remember when Defrag used to have a graphical illustration where all bad sectors were clearly marked. Perhaps I will look for some third-party defrag tool with this good old graphical part. Hovever it seems a bit overkill, a simple command should give me an overview of sectors marked as bad I would have thought.

Easeus Partition Manager has a tool "Check partition" which includes a test "Surface Test: Make detection of a disk or partition for sector errors. After the test completing, a report will be produced.". Sounds like I might have to wait 3 hours again (why can't I just get a list of what is already marked as bad?!) but it might work.
a b G Storage
December 28, 2012 8:55:00 PM

In win7 run a command prompt "as administrator" (right click icon) and chkdsk will give a full log. I haven't tried format. I too prerred the old simple graphics display of defrag and such. defrag /sd- /ss- is still ingrained in my head. There are lots of modern free utilities for those with an appreciation of the verbose.
December 29, 2012 6:20:56 AM

I ran "CHKDSK /B" in CMD window (opened as admin) on one of the drives. At the end it said "0kB in damaged sectors". So I guess that must mean there are no damaged sectors. Which means it is not the sector check (which I think is synonymous to "surface scan") that fixed my drives. So it must be something else, that "slow format" did to my drives.

And then I'm more or less back to the original question: What does "slow format" do that "quick format" and CHKDSK does not do?
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