Re: ata_eh_link_autopsy: Bug?

[Mark Lord <kernel@teksavvy.com>]

On 12-05-01 07:48 PM, Mark Lord wrote:
> On 12-05-01 05:58 PM, Tejun Heo wrote:
>> On Tue, May 01, 2012 at 04:27:00PM -0400, Mark Lord wrote:
>>> MMmm.. even that isn't good enough, because the first ATA_QCFLAG_IO test
>>> bypasses the rest of that logic and triggers unconditional retries.  Ugh.
>>
>> Hmmm... the unconditional retry on ATA_QCFLAG_IO is intenttional so
>> that known good requests from FS are guaranteed to be retried no
>> matter how whacky the underlying device is.  I'm not sure whether that
>> was a good decision tho.  Maybe we should trust the hardware a bit
>> more.  So, I'm not necessarily against changing it.
> 
> With multi-terabyte drives being commonplace now, bad sectors seem
> to be a more frequent occurrence than I can remember from the past.
> 
> And when libata stumbles across a bad sector, it literally hangs the
> machine for _minutes_ doing retries.  I have never seen a retry make
> any difference whatsoever on a bad sector read.  New, old, or ancient hardware.


And as a reminder to anyone else listening in,
it's easier than you might think to test failure paths like this.

Here, I keep a few 300GB drives around just for that purpose,
and use "hdparm --make-bad-sector" on them to inject media errors
at specific places on the disk or filesystem.

Cheers