Re: [patch] document flash/RAID dangers

[david]

On Wed, 26 Aug 2009, Pavel Machek wrote:

> On Tue 2009-08-25 17:20:13, david@xxxxxxx wrote:
> > On Wed, 26 Aug 2009, Pavel Machek wrote:
> >
> > > On Tue 2009-08-25 16:56:40, david@xxxxxxx wrote:
> > > > On Wed, 26 Aug 2009, Pavel Machek wrote:
> > > >
> > > > > There are storage devices that high highly undesirable properties
> > > > > when they are disconnected or suffer power failures while writes are
> > > > > in progress; such devices include flash devices and MD RAID 4/5/6
> > > > > arrays.
> > > >
> > > > change this to say 'degraded MD RAID 4/5/6 arrays'
> > > >
> > > > also find out if DM RAID 4/5/6 arrays suffer the same problem (I strongly
> > > > suspect that they do)
> > >
> > > I changed it to say MD/DM.
> > >
> > > > then you need to add a note that if the array becomes degraded before a
> > > > scrub cycle happens previously hidden damage (that would have been
> > > > repaired by the scrub) can surface.
> > >
> > > I'd prefer not to talk about scrubing and such details here. Better
> > > leave warning here and point to MD documentation.
> >
> > I disagree with that, the way you are wording this makes it sound as if
> > raid isn't worth it. if you are going to say that raid is risky you need
> > to properly specify when it is risky
>
> Ok, would this help? I don't really want to go to scrubbing details.
>
> (*) Degraded array or single disk failure "near" the powerfail is
> neccessary for this property of RAID arrays to bite.

that sounds reasonable

David Lang
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