FC5 RAID 1 - booting off either drive

[Craig White]

On Tue, 2006-03-28 at 20:20 -0600, Laurence Vanek wrote:
> Craig White wrote:
> > On Tue, 2006-03-28 at 08:05 -0700, Craig White wrote:
> >   
> >> On Mon, 2006-03-27 at 21:43 -0600, Laurence Vanek wrote:
> >>     
> >>> Greetings -
> >>>
> >>> To my surprise, fresh install of FC5 with RAID 1 configured at install 
> >>> time went without a hitch.  I have /dev/md0 defined on /boot 
> >>> partitions.  It boots fine with this setup.
> >>>
> >>> I had my FC4 system setup this exact way except I found that I had to 
> >>> manually install grub on one of the disks to permit booting off either 
> >>> one if the other is down.
> >>>
> >>> Does anyone know of a way to check for the presence of grub on each 
> >>> drive (obviously its on hda since it boots presently) to see if this 
> >>> needs to be done for FC5 also without powering down each drive in turn & 
> >>> attempting to boot?
> >>>       
> >> ----
> >> thought I should post against the right thread
> >>
> >> just an untested thought...
> >>
> >> bb if=/dev/sda of=/tmp/sda-bootblock.bin bs=512 count=1
> >> bb if=/dev/sdb of=/tmp/sdb-bootblock.bin bs=512 count=1
> >>
> >> diff /tmp/sda-bootblock.bin /tmp/sdb-bootblock.bin
> >>
> >> Thinking...
> >>
> >> - substitute different values for sda/sdb as fits
> >> - the first 512 bytes on each drive are the boot (perhaps less, someone
> >> will surely correct me...it might just be the first 256 or 384 bytes)
> >> - if they are the same (i.e. grub has been installed on both), there
> >> will be no diff
> >>
> >> otherwise...
> >>
> >> grub-install /dev/sdb
> >>
> >> Of course, the only way that you'll ever KNOW for sure that it's going
> >> to work is to do a real simulation, i.e. disconnecting one drive, then
> >> the other drive...
> >>     
> > ----
> > not only wrong thread but as Paul so correctly points out.
> >
> > dd - NOT bb
> >
> > I am rapidly ingesting coffee but haven't figured out a mainline method
> > so I am left to normal ingestion methods which apparently haven't quite
> > caught up to my fingers or my brain.
> >
> > duh.
> >
> > Sorry
> >
> > Craig
> >
> >   
> Followed your suggestion.  Boot sectors were NOT the same size on hda & 
> hdc (hdd is my CD-RW).  Same deal as with FC4.  I installed grub on my 
> second drive (hdc) using:
> 
> #grub
> grub>root (hd1,0)
> grub>setup (hd1)
> grub>quit
> 
> powered down, unplugged hda & VIOLA! (it boots).
> 
> Thanks for the help.
----
sure thing - just wondering (for completeness and all) - in case anyone
looks at the archives...

if you do...

dd if=/dev/hda of=/tmp/hda-512.bin bs=512 count=1
dd if=/dev/hdc of=/tmp/hdc-512.bin bs=512 count=1
diff /tmp/hda-512.bin /tmp/hdc-512.bin

do they match? (ie...diff comes up empty?)

How about as Aaron suggested...466 bytes...

dd if=/dev/hda of=/tmp/hda-466.bin bs=466 count=1
dd if=/dev/hdc of=/tmp/hdc-466.bin bs=466 count=1
diff /tmp/hda-466.bin /tmp/hdc-466.bin

do they match?

I can see a lot of occasions where the partition tables might not match
on the hard drives (such as Dell's utility partition being on /dev/hda
but not /dev/hdc or different brand drives, etc.)...

Craig