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La question
Le lecteur de SuperUser, Simon, est vraiment curieux de savoir quel sort il pourrait subir s'il n’éjecte jamais son média en toute sécurité:
Quite often when I’m in a rush, I automatically pull out a USB pendrive or USB cable from an external hard drive from my desktop PC or laptop, without right-clicking on the safely remove icon in the system tray and unplugging via this route. So far nothing untoward has happened every time I have “been in a rush”.
What is the rationale behind right clicking on the safely remove icon and can I really lose information on USB media if this is not carried out ?
Is the [probability] of losing such information greatly increased, if the USB media is still flashing at the time of pulling it out of the computer (as opposed to non-flashing) ?
Quel est le pari de Simon?
La réponse
Dave Rook, contributeur à SuperUser, explique:
Yes it can, it’s about what happens if you remove the device when it’s in use (reading or writing):
When you plug in a USB drive, you give your PC free rein to write and read data from it; some of which is cached.
Caching occurs by not writing information immediately to the USB device, and instead keeping it in your PC’s memory (RAM). If you were to yank the USB drive out of your PC before this information is written, or while its being written, you’ll end up with a corrupted file.
However, Windows automatically disables caching on USB devices, unless you specifically say that you want it enabled. For the most part you don’t have to click the ‘Safely Remove Hardware’ button, if you aren’t writing or reading anything from the device.
Its there simply as an extra level of security preventing you from destroying your own files.
Doing so causes the files to close “gracefully”, preserving data, pointers and file size indicators. When writing to disk the computer doesn’t always “flush” a buffer and only part of the data may have been written. Using the proper procedure will assure that the data and pointers are in good shape.
Source
MSalters offre un aperçu qui donne à réfléchir:
A second reason is that flash drives need to have stable power for ~0.25 seconds after a write command. This is a fundamental physical problem, due random factors some writes may leave a logical 1 bit in a electrical 0.72 state. The fix is easy: just rewrite the bit, perhaps even a few times. Eventually it will stick.
If you’re really unlucky, the bit falling over will be in a filesystem table and corrupt e.g. an entire directory.
En d'autres termes, il n'est pas intéressant de jouer avec quel bit peut ou peut ne pas être corrompu: il peut s'agir d'un fichier temporaire dans le cache d'une application portable ou il peut s'agir, comme le souligne MSalters, d'un fichier système critique.
Pour plus d'informations sur l'éjection sécurisée des supports, consultez: HTG explique: Avez-vous vraiment besoin de supprimer les clés USB en toute sécurité?
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