USB drive unmount

Gavin McCullagh gmccullagh at gmail.com
Tue Aug 7 18:41:57 BST 2007


Hi,

On Tue, 07 Aug 2007, Daniel Kahn Gillmor wrote:

> Richard Doyle <rdoyle at islandnetworks.com> writes:
> 
> > Fair enough. Now I just need to figure out how to get high school
> > students to wait until the device is done...

> AFAICT, that's the entire purpose of requiring users to "eject" a
> volume.  When you say "eject" (or whatever), it's a trigger to the OS
> to finish flushing any pending writes, followed by a clean unmount.

Exactly my understanding.

> With modern filesystems like ext3, as long as there are no pending
> write requests the lack of a clean unmount isn't a big deal: it just
> reviews the journal when it's re-inserted, and comes right back up.

Of course, the vast majority of external usb devices are FAT32 filesystems
to which this probably doesn't apply.

> Alternately, you could take the approach that Win95 took with floppy
> disks: no caching of disk writes was allowed.  If you did an operation
> which caused a write to the floppy (which was excruciatingly slow),
> the entire system would hang until the write was completed.  Between
> that and the grinding noise that active floppies make, you knew when
> you weren't supposed pop out the disk.  

I guess so long as the nautilus file copy window stays visible until all is
done, or the cp command doesn't complete or whatever, until it's safe to
remove most people will have the sense not to remove the disk.  In
particular beginner users tend in my experience to be very serial, waiting
for one thing to finish before doing the next.   However, I'm not sure
applications generally do guarantee this.

Is it actually possible to be certain when it's safe to remove a device?

Gavin




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