Re: [patch] document flash/RAID dangers

[david]

On Wed, 26 Aug 2009, Ric Wheeler wrote:

> On 08/26/2009 08:40 AM, Theodore Tso wrote:
> > On Wed, Aug 26, 2009 at 07:58:40AM -0400, Ric Wheeler wrote:
> > > > Drive in raid 5 failed; hot spare was available (no idea about
> > > > UPS). System apparently locked up trying to talk to the failed drive,
> > > > or maybe admin just was not patient enough, so he just powercycled the
> > > > array. He lost the array.
> > > >
> > > > So while most people will not agressively powercycle the RAID array,
> > > > drive failure still provokes little tested error paths, and getting
> > > > unclean shutdown is quite easy in such case.
> > >
> > > Then what we need to document is do not power cycle an array during a
> > > rebuild, right?
> >
> > Well, the softwar raid layer could be improved so that it implements
> > scrubbing by default (i.e., have the md package install a cron job to
> > implement a periodict scrub pass automatically).  The MD code could
> > also regularly check to make sure the hot spare is OK; the other
> > possibility is that hot spare, which hadn't been used in a long time,
> > had silently failed.
>
> Actually, MD does this scan already (not automatically, but you can set up a 
> simple cron job to kick off a periodic "check"). It is a delicate balance to 
> get the frequency of the scrubbing correct.

debian defaults to doing this once a month (first sunday of each month), 
on some of my systems this scrub takes almost a week to complete.

David Lang
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