Re: replacing a failed RAID component

[Stephen Borrill <netbsd%precedence.co.uk@localhost>]

On Sat, 7 Nov 2009, Steven Bellovin wrote:
> > On Sat, 7 Nov 2009, Steven Bellovin wrote:
> > > I'm using RAIDFRAME in a RAID 1 configuration.  One of the disks has 
> > > failed and needs to be replaced; the question is how, precisely, I do it. 
> > > More specifically, how do I prepare the new disk?  My assumption is that I 
> > > have to set up the proper fdisk label (including the boot block); I then 
> > > have to use disklabel to make the 'e' partition of type RAID.  The last 
> > > thing I should do is use 'raidctl -R' to reconstruct the RAID set.
> > >
> > > Do I need to do anything else?  Do I need to do something to initialize 
> > > the replacement disk's RAID stuff?
> >
> > A cheap hack is to use dd to copy the first few sectors (i.e. including mbr 
> > code, fdisk partition table and diskabel) from one disk to the other.
> >
> > Then use raidctl -a, raidctl -F, etc. to rebuild the array.
>
> -a and -F?  I was assuming I could just do -R.  I confess that I'm quite 
> unclear about the difference here.

-R fails a component (if necessary) and rebuilds back onto that component. 
-a adds a hot spare and then -F fails a component and rebuilds onto the 
hot spare. Chances are your components are currently something like 
/dev/wd0e and component1, you would need to add /dev/wd1e and then fail 
component1. You couldn't just use -R on the failed component as the new 
disk won't have the component label on it at boot time.

--
Stephen