Re: RAID 1 or Hammer

[Konstantinos Pachnis <kpachnis@xxxxxxxxxxx>]

On Jan 12, 2009, at 9:13 PM, Gergo Szakal wrote:

> "nntp.dragonflybsd.org" <mneumann@ntecs.de> wrote in message 496b8121$0$881$415eb37d@crater_reader.dragonflybsd.org">news:496b8121$0$881$415eb37d@crater_reader.dragonflybsd.org 
> ...
> > Hi,
> >
> > I'm curious if RAID 1 (mirroring) really helps to protect data  
> > loss. Of course if a whole disk "dies", RAID 1 has the advantage that
> > I have an identical copy. But what happens if only a sector of one  
> > disk
> > contains bad data. How can the RAID controller decide which is the
> > correct sector? Or would the disk detect such a case and return an  
> > error?

When the controller will try to perform an I/O operation it will fail  
on the faulty disk (the disk with the bad sector). As a result the  
controller will be able to decide which is the correct sector.


> IMHO RAID provides redundancy and higher data availability while  
> HAMMER mirroring
> provides data safety by by backups. Having a non-0 RAID array is not  
> equal to data
> safety IMHO. Only backups can provide that.
>
> Just my very own 0.02 though.