Re: getting I/O errors in super_written()...any ideas what would cause this?

[Ric Wheeler <rwheeler@redhat.com>]

On 12/05/2012 04:20 AM, James Bottomley wrote:
> On Tue, 2012-12-04 at 16:00 -0600, Chris Friesen wrote:
>> As another data point, it looks like we may be doing a SEND DIAGNOSTIC
>> command specifying the default self-test in addition to the background
>> short self-test.  This seems a bit risky and excessive to me, but
>> apparently the guy that wrote it is no longer with the company.
> This is a really bad idea.  A lot of disks go out to lunch until the
> diagnostics complete (the same goes for SMART diagnostics).  This means
> that if you do diagnostics on a running device, the drivers start to get
> timeouts on commands which are queued waiting for diagnostics to
> complete ... if those go over the standard SCSI timeouts, we'll start to
> try error recovery and likely have the disaster you see above.
>
>> What is the recommended method for monitoring disks on a system that
>> is likely to go a long time between boots?  Do we avoid any in-service
>> testing and just monitor the SMART data and only test it if something
>> actually goes wrong?  Or should we intentionally drop a disk out of the
>> array and test it?  (The downside of that is that we lose
>> redundancy since we only have 2 disks.)
> What do you mean by "monitoring" ... as in what are you looking for?  To
> make sure the disk is healthy and responding, a simple test unit ready
> works.  To look at other parameters, read the mode pages.
>
> Anything that actively causes the disk to go out and check something is
> a bad idea in a running environment.  Only do this if you can quiesce
> the I/O before starting the active diagnostic (or drop the disk from the
> array as you suggest).
>
> To be honest, though, modern disks do a whole host of diagnostics as
> they write data just to check that it is safely committed, so passive
> monitoring should be fine.
>
> James
>
>

I don't think that the basic stat gathering (smartctl -a ....) has this kind of 
impact, but am worried about the running of the diagnostics,

ric