FAT, FAT32 is not damage resistant and can vanish without much prodding.
I'm surprised no one wrote about using NTFS on such to get some damage resistance. However externals now have a fine track record of being less reliable than the internal drives. As to the warning, unless we enable SMART and even then we may get no warning.
Bob
Last spring I got a new laptop (expensive, business-class), and the operating system choice was Vista (or get a Mac). Or, it could be "downgraded" to XP. The desktop and two other laptops were on XP Pro. I also got a portable hard drive from the laptop mfgr. (and had been using several from Seagate over the previous 4-5 years with no issues). For the first few months, I used the portable drive only with the new laptop, and the new laptop with Vista issued permanent drive letters to each portable drive. When the new laptop required a repair (mouse button, which has been a repetitive 3-month issue since), I used the hard drive with one of the XP laptops. Shortly afterward, the portable drive failed, beginning with very little indication of a problem, and prompted for a reformat. It was replaced under warranty, but new information was lost. After the replacement drive came in, the laptop again needed a mouse repair, and I used the replacement portable drive on the XP laptop again. Here was my first clue that it may be related between going back and forth between the two operating systems. Next, the CD drives on the desktop quit working following an automatic update. The desktop was almost 5 years old, an IBM which was supposed to be very reliable, and had been until this. I took it into the same repair center and they resolved a registry error. After about two more boot cycles, BOTH hard drives failed without warning. Neither can be read. I had also used the portable drive with the desktop.
I ran across something online a while back about this being a known issue, but can't find that now. Are other users finding this to be a common problem, that drive failures occur when you move a portable drive between Vista and an XP systems? Is the FAT being corrupted by doing this?

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