DragonFly users List (threaded) for 2009-01
DragonFly BSD
DragonFly users List (threaded) for 2009-01
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Re: RAID 1 or Hammer


From: Konstantinos Pachnis <kpachnis@xxxxxxxxxxx>
Date: Mon, 12 Jan 2009 22:37:27 +0200


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.




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