Re: No I/O errors reported after SATA link hard reset

[Gionatan Danti <g.danti@assyoma.it>]

Hi Tejun,

Il 17-08-2017 14:48 Tejun Heo ha scritto:
> Recovered errors aren't reported as IO errors and at least from link
> state proper there's no way for the driver to tell apart link
> glitches and buffer-erasing power issues.

Ok, so *this* is the root cause of the problem: libata not identifying 
spurious link renegotiations vs brief powerloss/powerup events. Out of 
curiosity: is this a SATA-specific problem (ie: in the SATA 
specification), or even SAS disks are affected?

>> > - why the scsi midlevel does not respond to a power loss event by
>> > immediately offlining the disks?
> 
> Because we don't wanna be ditching disks on temporary link glitches,
> which do happen once in a while.

Any chances to report I/O errors to the upper layers *without* offlining 
the device? In this manner, upper layers (ie: MDRAID) can act in a more 
informate way. For example: single disk device will simple retry the 
failed operation, while MDRAID can take the "badblocks" code path to 
deal with the error.

> So, the right way to deal with the problem probably is making use of
> the SMART counter which indicates power loss events and verify that
> the counter hasn't increased over link issues.  If it changed, the
> device should be detached and re-probed, which will make it come back
> as a different block device.  Unfortunately, I haven't had the chance
> to actually implement that.

This is a very good idea, maybe I can implement it in userspace with a 
simple, fast polling scheme (for example, each 60 seconds). Such a 
polling would not prevent all corruption scenarios, but will at least 
timely inform the user.

Thanks.

-- 
Danti Gionatan
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