FC5 RAID 1 - booting off either drive

[Laurence Vanek]

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
>
>   
Craig -

my present drive condition is:

=========
[root at localhost tmp]# dd if=/dev/hda of=/tmp/hda-bootblock.bin bs=512 
count=1
1+0 records in
1+0 records out
512 bytes (512 B) copied, 8e-05 seconds, 6.4 MB/s
[root at localhost tmp]# dd if=/dev/hdc of=/tmp/hdc-bootblock.bin bs=512 
count=1
1+0 records in
1+0 records out
512 bytes (512 B) copied, 7.2e-05 seconds, 7.1 MB/s
[root at localhost tmp]# diff hda-bootblock.bin hdc-bootblock.bin Binary 
files hda-bootblock.bin and hdc-bootblock.bin differ
=============

although diff says they are different, I can boot off either with the 
other unplugged.  I guess the dd, diff method is not definitive.