How necessary is unmounting a USB memory stick

[freedom2009]

I have read that you need to unmount a USB memory stick before you unplug it.
Why is this necessary and what might happen if you don't unmount first?
I know it is easy to do using Dolphin, but it is easy to forget to do it. :P

[dibl]

Re: How necessary is unmounting a USB memory stick

Plug in a USB stick, and wait until it is recognized. Open Dolphin, find a file -- any file -- and copy it to the USB stick. Now, as soon as the copying message is finished, yank out your USB stick.

Next, plug your USB stick back in, and look for the file you thought you copied to it.

Probably this procedure will answer your question.

[kevinc]

Re: How necessary is unmounting a USB memory stick

This question has been answered in another post, but I couldn't locate it right now.

What happens when you write to a USB stick, or any other device or any other file, is that what you are writing first gets written to a buffer, a temporary storage place, and when the device is available and ready to receive the information is written to it.

Note, Memory is very fast, hard disks are fast but slower than memory and external USB devices are slower, I think maximum 12Gbit/second. With all the different speeds and faster devices needing to wait for slower ones, buffers are very handy, especially when burning a CD or DVD. Look next time you use K3B to burn a disk.

When the copy program has passed all of the information to the buffer it signals that it is finished.
If you want to remove the disk you must ask the OS - Kubuntu in this case, to empty the buffer before removing the device.

[kubicle]

Re: How necessary is unmounting a USB memory stick

Mounting with the 'sync' option is "safer" if you are in a habit of just yanking out your removable media...but it has a few drawbacks. So I'd recommend (like others on this thread) learning a new habit

[freedom2009]

Re: How necessary is unmounting a USB memory stick

Thanks
For me, it is easier to remember to do something if I know why it needs to be done

[Detonate]

Re: How necessary is unmounting a USB memory stick

Kevinc gave a good answer, let me add that there can also be an issue with the file allocation table (FAT) on the disk if it is not properly unmounted before removing and you could lose access to all of the files on the disk, not just the recent ones.

[Bottlecap]

Re: How necessary is unmounting a USB memory stick

Last year sometime, I had a weird experience with a USB thumbdrive. It is a 4GB gadget, but it started showing up as a much smaller device - only a few megabytes. After a LOT of messing with it, I was able to get the full capacity back.

I think this strange behaviour was caused by carelessly pulling it out of the USB port before it was ready.

[skunk]

Re: How necessary is unmounting a USB memory stick

I concur. Removing a USB device before changes have been synched has resulted in devices that were unusable until they were reformatted.