Re: Four Drive RAID-5 on RAIDFrame Considered Harmful...

On Wed, Oct 10, 2007 at 02:59:37PM -0600, Greg Oster wrote:
> Greg Troxel writes:
> > Because of this I've always just bought two big disks and done RAID-1.
> 
> RAID 1 has the same issue -- Say the machine dies at the point where
> block n is written to component 0 but not to component 1.  If 
> component 0 dies before block n gets synced between the two, then 
> when you read block n from component 1, you're going to get the old 
> data.

I am curious - what do the BIOS-based software RAID controllers (as
offered by e.g. Promise and supported by ataraid(4)) do to correct the
situation when block n is written to component 0 but not 1? AIUI, you have
to do a re-sync after such unclean shutdown (hoping that the component
won't die before the data are synced) or have a battery backed cache.
So, do those "RAID controllers" re-sync parity after unclean shutdown?

Pavel