Re: [PATCH] USB: storage: add "no SYNCHRONIZE CACHE" quirk

[Stefan Richter <stefanr@s5r6.in-berlin.de>]

On Jun 26 James Bottomley wrote:
> On Fri, 2015-06-26 at 11:43 +0200, Stefan Richter wrote:
> > On Jun 22 James Bottomley wrote:
[...]
> > > Perhaps it might be wise to do this to every USB device ... for external
> > > devices, the small performance gain doesn't really make up for the
> > > potential data loss.
> > 
> > Just a small note on the assumption of externally (and in extension,
> > temporarily) attached devices:  Not all USB-attached devices are external,
> > and not all external devices are used as removable devices.
> 
> The problems don't depend on the connection type: internal devices which
> have a writeback cache and don't accept flush commands have data
> integrity problems too.  I can't really think of many situations where
> you'd be willing to sacrifice data integrity for performance.

Sure; writeback caches are prone to more issues besides sudden connection
loss.  (E.g. sudden power loss is but one of several more potential issues
of course.)

I merely wanted to remind that the bus type of a device (USB or whatever)
does not say much about the risk of sudden connection loss to that device,
since such devices may have physical protection against sudden connection
loss too.  I was not particularly commenting on the topic at hand, i.e.
on presence of writeback cache without working flush command.
-- 
Stefan Richter
-=====-===== -==- ==-=-
http://arcgraph.de/sr/