4
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?
RomanSt
Posted 2009-08-20T12:12:06.297
Reputation: 7 830
7
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.
jweede
Posted 2009-08-20T12:12:06.297
Reputation: 6 325
3How/why is it safer to remove a FAT drive versus an NTFS drive without unmounting? – Breakthrough – 2011-06-30T17:13:29.783
1It'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 – 2011-07-01T03:03:43.050
6
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.
fretje
Posted 2009-08-20T12:12:06.297
Reputation: 10 524
By default Write caching is disabled in Windows for external drives. This ensures you can safely remove the drive without first un-mounting the drive. You can find the appropriate options in the device properties Policies tab. http://i.imgur.com/ikhcImP.jpg
– jduncanator – 2017-07-14T00:16:33.993I 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 – 2011-01-25T00:13:34.403
@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 – 2011-02-01T10:27:01.973
1
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.
OverCertified
Posted 2009-08-20T12:12:06.297
Reputation: 131
Write caching is disabled by default for external drives under Windows. – jduncanator – 2017-07-14T00:17:20.287
1
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.
Tom Corelis
Posted 2009-08-20T12:12:06.297
Reputation: 303
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 – 2011-08-10T01:06:08.743