[CentOS] Re: Rebuilding Raid 1

[Les Mikesell]

On Tue, 2006-05-02 at 00:13, Mace Eliason wrote:
> I think the reason for the partitions not being on the same drive is 
> because the old drive is the bootable drive and I changed the scsi ids 
> of the drives to get it to work.   I think it is using sba for the boot 
> but centos is on sbb. 

It doesn't really boot from raid.  It loads the kernel from
the underlying partition on the boot drive, then the kernel
detects the raid devices and decides how to activate them,
then it mounts them according to /etc/fstab.  You should be
able to review the detection process with 'dmesg |less'
if you are interested.

> I just need to make sure that the sync happens so that the info on sbb 
> is what is synced.  The info on sba is 1 month old this I have confirmed 
> by mounting sba3 and looking at the dates of the last emails received on 
> the server  I couldn't mount sdb3 because it is the active partition.

Be careful with your spelling... I assume you mean /dev/sda3 is the
old one.  

> So from what your saying below running mdadm as you have shown will it 
> copy the good info on sdb to sda?

Again, be careful.  It will copy the currently active partition
to the one you are adding - so if you see the current version
now, that's what will be mirrored.  In the case of /dev/sdb3 it
will go from sdb to sda.   But /dev/sda1 is active now and will
be copied to /dev/sdb1.

> I have to have this server ready for 7am or we will loose this 
> contract.  I can't believe I have spend all day on this.

This is the sort of thing you should practice on a test
box so you are prepared to handle an actual problem in a
reasonable amount of time.

> If I copy over the wrong info they will lose 1 months worth of emails.

You can only copy from the active one to the one you
add.  And by the way, having backups can be a good thing
too...

-- 
   Les Mikesell
     lesmikesell at gmail.com