On Tue, 15 Dec 2015, Oliver Neukum wrote:

> On Thu, 2015-12-03 at 13:36 -0500, Alan Stern wrote:
> > This is an old problem, but it was never resolved and it still affects
> > people (Bugzilla #89511).  In short, there are USB-(S)ATA bridges that
> > claim to be write-back but don't support the SYNCHRONIZE CACHE
> > command.  
> > This causes errors when filesystems try to flush data out to the disk.
> 
> OK, maybe this is a stupid idea, but could we test the command as we
> enumerate the slave and store the result?

Maybe, although doing so within usb-storage would be kind of difficult
-- that driver is set up to forward requests from the SCSI layer, not
to generate requests of its own.  Besides, usb-storage doesn't know 
anything about write-back vs. write-through; only sd does.  I suppose 
sd could perform that test.

Alan Stern

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