"Assuming drive cache: write through" messages probably have wrong loglevel
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https://bugzilla.kernel.org/show_bug.cgi?id=16490
Tejun Heo <[email protected]> changed:
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Component|Serial ATA |SCSI
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https://bugzilla.kernel.org/show_bug.cgi?id=16490
Alain Kalker <[email protected]> changed:
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--- Comment #8 from Alain Kalker <[email protected]> ---
I submitted a patch to lower the log level to the linux-scsi mailing list. The patch was not accepted; James Bottomley offered this very insightful explanation why the log level should remain high (quoted here for those who are not reading the linux-scsi mailing list):
Quoted 11 lines
[...] The condition may be an error. We have
some USB attached storage devices with writeback caches which don't supply caching information. Treating a writeback device as writethrough is a potential error because you may lose data as a result of it.The error is that we've made an assumption which may damage your data.
The problem for us is that we can't tell if the assumption is going to be fatal or not ... the message is harmless for older USB devices.
From doing a little research, I would suggest these steps to mitigate the risk
(correct me if I'm wrong or have omitted anything):
- Find out if the device has write cache enabled by default, by consulting its documentation, technical specifications, or by contacting the manufacturer.
- If the device does have write cache enabled, a quirk parameter can be added to either the kernel commandline or as a module parameter for the usb-storage module[1]
- Verify that the device works as expected.
[1] For more information on USB storage device quirks and how to configure them, see linux/Documentation/kernel-parameters.txt in the Linux kernel source.
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