Re: [patch] ext2/3: document conditions when reliable operation ispossible

[Ric Wheeler]

On 08/26/2009 07:12 AM, Pavel Machek wrote:
> On Wed 2009-08-26 06:39:14, Ric Wheeler wrote:
>    
> > On 08/25/2009 10:58 PM, Theodore Tso wrote:
> >      
> > > On Tue, Aug 25, 2009 at 09:15:00PM -0400, Ric Wheeler wrote:
> > >
> > >        
> > > > I agree with the whole write up outside of the above - degraded RAID
> > > > does meet this requirement unless you have a second (or third, counting
> > > > the split write) failure during the rebuild.
> > > >
> > > >          
> > > The argument is that if the degraded RAID array is running in this
> > > state for a long time, and the power fails while the software RAID is
> > > in the middle of writing out a stripe, such that the stripe isn't
> > > completely written out, we could lose all of the data in that stripe.
> > >
> > > In other words, a power failure in the middle of writing out a stripe
> > > in a degraded RAID array counts as a second failure.
> > >     To me, this isn't a particularly interesting or newsworthy point,
> > > since a competent system administrator who cares about his data and/or
> > > his hardware will (a) have a UPS, and (b) be running with a hot spare
> > > and/or will imediately replace a failed drive in a RAID array.
> > >        
> > I agree that this is not an interesting (or likely) scenario, certainly
> > when compared to the much more frequent failures that RAID will protect
> > against which is why I object to the document as Pavel suggested. It
> > will steer people away from using RAID and directly increase their
> > chances of losing their data if they use just a single disk.
> >      
> So instead of fixing or at least documenting known software deficiency
> in Linux MD stack, you'll try to surpress that information so that
> people use more of raid5 setups?
>
> Perhaps the better documentation will push them to RAID1, or maybe
> make them buy an UPS?
> 									Pavel
>    

I am against documenting unlikely scenarios out of context that will 
lead people to do the wrong thing.

ric


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