>Well, umount is not the "right" way to do it, so he'd be simulating a
>power-loss/system-crash. That still doesn't explain why massive data loss
>would occur ? I would understand the last txg being lost, but 90% according
>to OP ?!
On USB or? I think he was trying to properly unmount the USB devices.
One of the known issues with USB devices is that they may not properly
work; for a typical disk, it will properly "flush write cache" when it
is instructed to do so.
However, when you connect the devices using a USB controller and a USB
enclosure, we're less certain that "flush write cache" will make it
to the drive, because:
- was a command send to the enclosure (e.g., if you needed to configure
the device with "reduced-cmd-support=true", then all bets are
off)
- when the enclosure responds, did it send a "flush write cache"
to the disk?
- and when it responds, did it wait until the disk completed the
command?
It is one of the reasons why I'd recommend against USB for disks. Too
many variables.
Casper
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