Soft-Raid Testing and other stuff...

[Richard Hobbs]

Hello,

> -----Original Message-----
> From: redhat-list-bounces at redhat.com 
> [mailto:redhat-list-bounces at redhat.com] On Behalf Of Richard Hobbs
> Sent: 20 January 2005 14:23
> To: 'General Red Hat Linux discussion list'
> Subject: RE: Soft-Raid Testing and other stuff...
> 
> Hello,
> 
> > -----Original Message-----
> > From: redhat-list-bounces at redhat.com 
> > [mailto:redhat-list-bounces at redhat.com] On Behalf Of Ed Wilts
> > Sent: 20 January 2005 12:53
> > To: General Red Hat Linux discussion list
> > Subject: Re: Soft-Raid Testing and other stuff...
> > 
> > On Thu, Jan 20, 2005 at 11:17:01AM -0000, Richard Hobbs wrote:
> > > > > I didn't duplicate the MBR as far as I know... I 
> > assumed that RAID 1
> > > > > (mirroring) mirrored the entire disk, sector for sector...
> > 
> > Nope - it's partition by partition.  That's why you did the 
> raidhotadd
> > *per partition*.
> > 
> > There are pros and cons to this approach - the biggest pro 
> is that you
> > don't have to mirror the entire disk.  The biggest con is 
> > that only data
> > partitions are mirrored.
> > 
> > For details on mirror the mbr, see:
> > http://www.dur.ac.uk/a.d.stribblehill/mirrored_grub.html
> > 
> > I haven't tried this but it's referenced by the online Red Hat
> > documentation.
> > 
> > > > > Also, if I then insert a blank disk, will it automatically 
> > > > > re-generate the
> > > > > data onto it? Will I have to duplicate the MBR manually again?
> > > > > 
> > 
> > You will always have to do this manually.  Software RAID 
> knows nothing
> > about the MBR - only partitions.
> 
> So... am I correct in saying that if I run 'raidhotadd' on 
> all partitions to
> get them mirrored correctly, and then I run the grub stuff to 
> install the
> slave MBR, all is set and there's absolutely nothing else 
> that needs to be
> done? In order to have a fully resilient system?
> 
> I realise the BIOS might need to be altered to tell it to 
> boot from the
> slave if the master is dead, but apart from that, is 
> everything done that
> needs to be?
> 
> Also, what are the exact steps to follow if the master disk dies in a
> soft-raid 1 environment?
> What are the steps to follow if the secondary disk dies in a 
> soft-raid 1
> environment?
> 
> I assume they are fairly similar... Just replace the dead disk with an
> identical blank one, boot up and reinstall the MBR once the automatic
> reconstruction is done, right?? Or is it not that simple...
> 
> Thanks again,
> Hobbs.

I have now solved this problem completely, so thanks to Ed Wilts and
SpookyEddy from TechIMO.com.

The answer was basically that I have to mirror the partitions independantly,
and I have to duplicate the MBR.

Also, if a disk fails, I have to manually re-create the partitions on the
blank disk exactly as they are on the working disk.

The full answer can be found here:

  http://unixforum.co.uk/667.html

Thanks to all :-)

Hobbs.

-- 
Richard Hobbs (Systems Administrator)
Toshiba Research Europe Ltd. - Speech Technology Group
Web: http://www.toshiba-europe.com/research/
Email: richard.hobbs at crl.toshiba.co.uk
Tel: +44 1223 376964        Mobile: +44 7811 803377



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