[CentOS] Re: Add RAID after install in one disk

Thu Mar 1 00:46:03 UTC 2007
James Olin Oden <james.oden at gmail.com>

On 2/28/07, Scott Silva <ssilva at sgvwater.com> wrote:
> James Olin Oden spake the following on 2/28/2007 9:27 AM:
> > On 2/28/07, Scott Silva <ssilva at sgvwater.com>
> > wrote:
> >> CM spake the following on 2/28/2007 5:40 AM:
> >> >> IIRC, you also have to do some special magic with the grub config to
> >> >> make the machine boot nicely even if you have to reboot with one drive
> >> >>
> >> >> down. Unfortunately, it's been a while since last time I did this, so
> >> >> I  can't remember.
> >> >>
> >> >> --
> >> >>   Haakon Gjersvik Eriksen     --                  Basefarm AS
> >> >
> >> > Presuming sda first HDD, sdb second HDD, first partition (0)  is /boot
> >> >
> >> > grub
> >> > device (hd1) /dev/sdb
> >> > root (hd1,0)
> >> > setup (hd1)
> >> >
> >> > CM
> >> >
> >> I'm confused. Wouldn't you want "root (hd0,0)"
> >> because if the first drive fails, the second drive will become sda
> >> after boot.
> >>
> > As I understand it the first drive does not become sda/hda after boot
> > in all cases.  At least with IDE drives it will always stay where it
> > is based on controller and master/slave relationship.   Beyond this,
> > though, when specifying "root" for the setup command grub taking the
> > drive in the context of how the BIOS has mapped who is the 0th, 1st,
> > 2nd and so on, with a simple transform provided by your
> > /boot/grub/device.map file.  At least this is what I believe to be the
> > truth.
> >
> > ...james
> IDE drives will stay where they are, but scsi and sata drives will move based
> on (for scsi) device id, and for sata would be a crap shoot but maybe by port
> (probably bios, driver, and controller dependent).
>
> But with an IDE drive, the slave might not be able to function unless the
> failed master is physically removed. If all drives are a master on their
> controller, it would be much better.
>
That sounds like what I recall.

so seriously, say have two drives mirrored, and you wish the machine
to boot without intervention if one of the drives goes, is their a
right grub configuration for each of the drive types (ide, sata, scsi)
and is it identical between each of the drive types are different?

I figure once your booted your fine because of UUID's.

Thanks....james