Messages in this thread | | | Date | Tue, 4 Nov 2008 20:57:29 +0100 | From | Pavel Machek <> | Subject | Re: data corruption: revalidating a (removable) hdd/flash on re-insert |
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On Fri 2008-10-31 17:10:26, Kay Sievers wrote: > On Fri, Oct 31, 2008 at 16:38, Michael Tokarev <mjt@tls.msk.ru> wrote: > > To make a long story short: is there a way to force kernel > > to re-validate a replaced usb-connected hard drive (or a > > flash) *automatically*? > > > > Because right now, the kernel does not see that the drive > > has been replaced, and uses *some* old cached values, which > > results in random data corruption here and there, and other > > similar odd things. > > Maybe your card reader is broken. I can not reproduce this with any of > the many readers I have. Usually a media change results in media > revalidation with the next access to the device. You can easily > reproduce that: > > Insert the media, and force a validation: > $ touch /dev/sdb > > Start logging of the kernel uevents to the console: > $ udevadm monitor --kernel & > > Access the device: > $ touch /dev/sdb > > Nothing should happen, as the reader/kernel knows it is still valid. > > Now remove the media and insert it immediately again. > > Access the device: > $ touch /dev/sdb > UEVENT[1225468868.803950] change > /devices/pci0000:00/0000:00:1d.7/usb5/5-2/5-2:1.0/host8/target8:0:0/8:0:0:0 > (scsi) > > and you see the reader told to kernel (scsi unit attention) to > revalidate the device. > > These events happen only when the device is accessed. That's why > distros poll removable devices for media changes. > > Every access to removable media is guarded by this revalidation check. > If you don't see these events, you should not trust this reader, and > at least never change the media while it is connected.
This is rather nasty data-corrupter. Could we at least blacklist broken device, and force revalidation on each close or something like that?
-- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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