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

Thu Mar 1 00:26:31 UTC 2007
Scott Silva <ssilva at sgvwater.com>

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.