Re: [PATCH RESEND v2] scsi: ignore Synchronize Cache command failures to keep using drives not supporting it

[Guido Trentalancia <guido@trentalancia.com>]

On Mon, 01/03/2021 at 12.57 +0000, Damien Le Moal wrote:
> On 2021/03/01 21:52, Guido Trentalancia wrote:
> > As already said, I have tested the patch for over a year now and I
> > have
> > never experienced the problem that you are foreseeing !
> 
> That may be true for your specific drive, but since we are in
> uncharted
> (non-standard) territory here, we cannot say that this will hold for
> all such
> weird drives out there.

I do not work in the hard drive industry, so I cannot make assumptions
about all existing models.

All patches should normally undergo further testing and this is no
exception.

I would stress once again that the proposed patch disables write
caching as soon as it realizes that the drive does not support the Sync
Cache command, so it has been designed to be extra safe.

> > The current alternative is data corruption each time that the drive
> > is
> > mounted and the inability to use it.
> > 
> > So, the patch is the way forward for using such drives plug and
> > play
> > without cumbersome configuration such as disabling the write cache,
> > which advanced users can always make.

[...]

> As mentioned, the alternative is a udev rule to disable write cache.
> Or if the
> drive supports that, permanently save WCE=0 setting in the drive
> config so that
> it always come up with write cache disabled. No kernel patch needed,
> and you
> will note that this is also exactly the same as what your patch does,
> without
> waiting for an error.

The above is cumbersome, the kernel should support such drives plug and
play, without causing data corruption which is happening at the moment.

Guido