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Is "Quick Format" safe?

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f0dder:
40hz: I definitely remember using /u back in the old DOS and w9x days - and iirc it was super slow. So I think (:)) it's more a case of /u actually zero-filling the partition rather than "not saving recovery information". Iirc the regular format didn't even completely nuke the FAT filesystem structures, but rather set every file&folders as deleted (done on FAT by setting the first char of it's name to some special character).

40hz:
You could be right. I just remember if you didn't do a /u on a floppy format, you wound up with less available disk space than if you did. Supposedly some hidden file(s) got saved that the unformat command could use to undo the format. When MSoft dropped the unformat command back around WinME (or thereabouts? Maybe it was still back in the late DOS days?) the /u became sort of meaningless.

I suppose you could try it on a floppy to see if it still does anything. I'm guessing these days it's just a "zombie switch" (i.e. doesn't violate command syntax, but also doesn't do anything).

That's assuming anybody still has a working floppy drive and usable media to test it!  ;D

f0dder:
Hm, could be you're right - if "unformat" was able to restore file/folder names without mangled first-char, then probably a copy of the FAT was saved, or just the file names. I wonder if this was only for floppies, or disk partitions as well?

40hz:
OK, I stopped being lazy and ran over to TechNet.

Here's what they had to say:

Safe formatting

If you do not specify the /u switch or a switch that reformats the disk to a different size, format performs a "safe" format. It clears the file allocation table and root directory of the disk but does not delete any data. You can then use the unformat command to recover the disk if you did not intend to format the disk. Format also checks each sector on the disk to ensure that the sector can properly store data. If it locates a sector that cannot store data, format marks that sector to prevent MS-DOS from using it.

If you specify the /u switch or any switch that changes the size of the disk, format performs an unconditional format by deleting all data on the disk.

Quick formatting

You can speed up the formatting process by using the /q switch. Use this switch only if you have not received read or write errors on your disk. You can speed up the process even more by using both the /q and /u switches. If you use the /u switch, format does not save the information necessary to later unformat the disk.
--- End quote ---

So I guess the "hidden recovery file" stuff I was told (or imagined being told  ;D) is incorrect. Looks like regular format (at that point) simply tossed the FAT and root directory. Kinda like "keeping all the library books and just throwing out the cardfile" as the saying used to go.

Still doesn't explain why a floppy always came up a few kilobytes short if you didn't do the /u (maybe it did keep a copy of the FAT/root after all?) but there you have it.

 :Thmbsup:

4wd:
This is somewhat of a shock to me - first, because this means a format doesn't wipe your data. Second, because new bad sectors might not be discovered merely from a read, and sector reallocation only kicks in on a write. Eek.

Thanks for making me look into this, Joker - I'll be sure to do an explicit single-pass wipe instead of format from now on.
-f0dder (November 16, 2010, 06:59 AM)
--- End quote ---

You could always try a Low Level Format, it worked on my 1TB Samsung - took a very long time, probably the same amount as doing a single-pass wipe.

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