RE: Soft-Raid Testing and other stuff...

richard.hobbs_at_crl.toshiba.co.uk

To: "'General Red Hat Linux discussion list'" <redhat-list@redhat.com>
Date: Wed, 20 Apr 2005 12:42:04 +0100


-- 
Richard Hobbs (Systems Administrator)
Toshiba Research Europe Ltd. - Speech Technology Group
Web: http://www.toshiba-europe.com/research/
Email: richard.hobbs@crl.toshiba.co.uk
Tel: +44 1223 376964        Mobile: +44 7811 803377 
> -----Original Message-----
> From: redhat-list-bounces@redhat.com 
> [mailto:redhat-list-bounces@redhat.com] On Behalf Of Richard Hobbs
> Sent: 21 January 2005 17:02
> To: 'General Red Hat Linux discussion list'
> Subject: RE: Soft-Raid Testing and other stuff...
> 
> Hello,
> 
> > -----Original Message-----
> > From: redhat-list-bounces@redhat.com 
> > [mailto:redhat-list-bounces@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@redhat.com 
> > > [mailto:redhat-list-bounces@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@crl.toshiba.co.uk
> Tel: +44 1223 376964        Mobile: +44 7811 803377
> 
> 
> 
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RE: Soft-Raid Testing and other stuff...

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