Re: [PATCH v2 5/5] dax: handle media errors in dax_do_io

[Dan Williams]

On Tue, Apr 26, 2016 at 1:27 AM, Dave Chinner <david@xxxxxxxxxxxxx> wrote:
> On Mon, Apr 25, 2016 at 09:18:42PM -0700, Dan Williams wrote:
[..]
> It seems to me you are focussing on code/technologies that exist
> today instead of trying to define an architecture that is more
> optimal for pmem storage systems. Yes, working code is great, but if
> you can't tell people how things like robust error handling and
> redundancy are going to work in future then it's going to take
> forever for everyone else to handle such errors robustly through the
> storage stack...

Precisely because higher order redundancy is built on top this baseline.

MD-RAID can't do it's error recovery if we don't have -EIO and
clear-error-on-write.  On the other hand, you're absolutely right that
we have a gaping hole on top of the SIGBUS recovery model, and don't
have a kernel layer we can interpose on top of DAX to provide some
semblance of redundancy.

In the meantime, a handful of applications with a team of full-time
site-reliability-engineers may be able to plug in external redundancy
infrastructure on top of what is defined in these patches.  For
everyone else, the hard problem, we need to do a lot more thinking
about a trap and recover solution.