RAID 1 or Hammer

[Konstantinos Pachnis]

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

"nntp.dragonflybsd.org" <mneumann at ntecs.de> wrote in message 496b8121$0$881$415eb37d at crater_reader.dragonflybsd.org">news:496b8121$0$881$415eb37d at 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.