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I'm hitting the 4GB limit of FAT32 on USB drives more and more often. However, being able to unplug the device without unmounting it first is a must have for me. I've noticed exFAT recently, however I couldn't find any info on whether drives formatted with exFAT can be unplugged safely without unmounting.

Can they?

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Any flash drive must be unmounted first. Flash is quite notorious for causing widespread data damage if unplugged while still writing, and the underlying physical process may take up to 2 seconds (especially with cheap MLC flash). This corruption is due to the fact that flash internally uses 128kB+ blocks, and remaps those rather randomly for "wear leveling purposes". You could corrupt 256 files that way. –  MSalters Aug 10 '11 at 1:06

4 Answers 4

up vote 6 down vote accepted

While it is not 100% safe to remove a FAT volume without unmounting, it is safer than NTFS.

exFAT has the following differences to FAT 32:

  • File size limit is now 16 exabytes.

  • Format size limits and files per directory limits are practically eliminated.

  • Like HPFS, exFAT uses free space bitmaps to reduce fragmentation and free space allocation/detection issues.

  • Like HTFS, permission systems should be able to be attached through an access control list (ACL). It is unclear if or when Vista will include this feature, however.

Since caching is handled much in the same way, you should get the same unmounting behavior from exFAT as you did from FAT32.

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How/why is it safer to remove a FAT drive versus an NTFS drive without unmounting? –  Breakthrough Jun 30 '11 at 17:13
    
It's true I didn't give much justification for that. As one of the other answers stated, NTFS often buffers writes which can lead to uncommitted changes when one saves a file. –  jweede Jul 1 '11 at 3:03

I'd heard somewhere that on *nix style OSes, I/O caching is done in such a way that it is much less safe to unplug a disk then on Windows.

In my own experience, I have corruption issues (requiring a good fscking) semifrequently when I unplug drives in OSX. I rarely, if ever, have those issues in Windows, under both FAT32 and exFAT.

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NTFS is not meant for removable drives. exFAT was designed for this, but keep this in mind: FAT12/FAT16 & FAT32 have 2 FAT's, they flip-flop. exFAT has one FAT, and if it gets corrupted, you're screwed. In a later release of exFAT there will be TexFAT (Transaction Safe exFAT) where there will be 2 FATs and 2 allocation bit maps. It will be safer.

But not unmounting is a risk, but less of a risk than NTFS because NTFS is lazy write and doesn't write everything out immediately, it bussers it.

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Not really specific to exFAT but:
I'd say it's NEVER really safe to unplug an USB drive without unmounting it first. At least when you've written stuff to the disk. As long as you're only reading, unplugging without unmounting can do no harm, but the moment you've actually written something onto the disk, you have to unmount it for the buffers to be flushed (It's possible that not everything is written yet to the disk).
If you wait long enough, they will be flushed, and it would be safe again to unplug without unmounting.

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I believe you are giving a *nix answer to what was intended as a Windows question. (At least, Windows does not generally behave in the manner you describe with FAT filesystems, whereas Linux does.) –  SamB Jan 25 '11 at 0:13
    
@SamB: What do you mean? This answer wasn't really meant to be specific to any platform... but I know it's like this on Windows. –  fretje Feb 1 '11 at 10:27

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