Migrating to software raid on fc3

[Sam Varshavchik]

Eric Persson writes:

> 1. install one new drive as a mirrored software raid with one missing disk.
> 2. either mount the old drive as readonly manually and then use dd to 
> move everything to the new md0 disk.
> 3. install bootloader on the new disk.
> 4. remove the faulty disk and boot on the new md0
> 5. install the second new disk and add it to the md0.
> 
> Would this be possible at all, I havent tried it in practice yet, but 
> will probably to it on a live server which will bring it to a certain 
> downtime.

This is doable, but the bootloader is going to be very tricky to set up.  
It's going to depend on whether the old/new hard drives are IDE or SCSI, 
and, if IDE, whether both drives plug into the same IDE channel, or one 
drive per channel.

When you're still booting off your old/failing drive, the old drive comes up 
as the first hard disk, and your new drive as the second hard disk.  When 
you install the bootloader, that's what the saved drive mapping will be.

When you swap the old drive for the new one, the new drive will come up as 
the first hard disk, but the bootloader will still expect the kernel and 
initrd to come off the second hard disk in the system.

There might be some advanced grub settings that you can specify beforehand 
to explicitly set the drive mapping, when grub gets installed.  Rooting 
around grub docs may find something.  The alternative is to boot the FC 
install disk in rescue mode, after swapping the drives.  The rescue mode 
should find your new partitions, and mount them.  Then, you chroot to the 
root partition on the hard drive and reinstall the bootloader; with the 
correct drive mappings.


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