RAID1 synchronisation - howto OR not necessary?

[Christian Walther]

Hi,

On 23/11/2007, Jan Catrysse <j.catrysse at proximedia.be> wrote:
> > From: Bill Moran [mailto:wmoran at potentialtech.com]
> > Sent: Thursday, November 22, 2007 9:57 PM
> > To: Jan Catrysse
> > Cc: freebsd-questions at freebsd.org
> > Subject: Re: RAID1 synchronisation - howto OR not necessary?
> >
> > "Jan Catrysse" <J.Catrysse at proximedia.be> wrote:
> > >
[...]
> This is what I found in a 3Ware manual:
> Verification can provide early warning of a disk drive problem or failure.
[...]
Yes, it deals with drives failing silently. It's possible that data on
a disk can get corrupted. You don't see the error until you read the
block the next time. AFAIK the data contained in the bad block is
delivered to the CPU/RAM and can cause some damage there.
The problem I see with this setup is that you can't know which block
is the one that is okay. You need some additional feature like a
checksum for each block to check which one is correct. This isn't
supported by all file systems, so you can only see that there is a
difference between two blocks which sould normally be identical.

I doubt that cheep RAID-Controllers have this capability, so you have
to stick to some software solution. Does FreeBSD take care about
something like this, I mean for software RAIDs?

Regards
Christian