From mboxrd@z Thu Jan 1 00:00:00 1970
From: bugzilla-daemon@bugzilla.kernel.org
Subject: [Bug 89511] USB-storage mount error
Date: Fri, 05 Jun 2015 14:54:18 +0000
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https://bugzilla.kernel.org/show_bug.cgi?id=89511
--- Comment #51 from Alan Stern ---
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.)
On Thu, 4 Jun 2015 bugzilla-daemon@bugzilla.kernel.org wrote:
> --- Comment #50 from Markus Rathgeb ---
> I ran in the same trouble with an old USB case for 2.5'' IDE hard discs.
>
> The drive cache_type is 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.
>
> 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
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