USB-storage mount error
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For those new to this bug report, the interesting part starts here:
https://bugzilla.kernel.org/show_bug.cgi?id=89511#c19
In short, these are USB drive adapters that doesn't support the SYNCHRONIZE CACHE command but claim to be write-back. (In at least one case, it initially claims to be write-through but then changes to write-back following a reset, or something like that.)
Quoted 9 lines · On Thu, 4 Jun 2015 [email protected] wrote:
--- Comment #50 from Markus Rathgeb <[email protected]> --- I ran in the same trouble with an old USB case for 2.5'' IDE hard discs.
The drive
cache_typeis set to "write back" if it plugged in. The drive is working using if I set the cache type to "temporary write through".So, I think this is the exact same problem discussed here.
Quoted 7 lines
At the moment I tested the workaround using v3.18.2 (gentoo-sources). Without the workaround the problem also exists using the Kernel v4.0.4 (used gentoo-sources, but I think that should not be related to the problem at all).
Is there anything I / we can do, to solve this problem at all in the kernel space (e.g. if SYNCHRONIZE CACHE command is not working, fallback to write through)?
This is up to the SCSI developers.
The real question is what should happen when a drive really does have a write cache but doesn't recognize the SYNCHRONIZE CACHE command. I don't know what the kernel can do in this case -- maybe just log a one-time error message and turn off sdkp->WCE?
Alan Stern