I think I have solved my issue and would like some input from anyone who has done this for pitfalls, errors, or if I am just wrong.

Centos 5.x, software raid, 250gb drives.

2 drives in mirror, one spare. All same size. 2 devices in the mirror, one boot (about 100MB), one that fills the rest of disk and contains LVM partitions.

I was thinking of taking out the spare and adding a 500gb drive. I would run this " sfdisk -d /dev/sda | sfdisk /dev/sdc " (drive 'a' setup is cloned onto drive c) Then I would add drive c to the raid array as the spare. I would then pull out drive b and allow drive c to be synced with a.

At this point drive c has 250gb worth of partioned space in raid/lvm.

I then add a 500gb drive b and repeat above pulling out drive a.

Now I have two 500gb drives (b and c) with 250gb worth of partitions mirrored.

I am thinking I would next forget about md0 (the boot part) and concentrate on the md1, where the whole system lies.

# mdadm --grow /dev/md1 --size=max

I believe this will grow out the size of md1 to fill the 500gb of the drive. I would then wrestle with expanding the LVMs that fill the md1 up as I wish.

After that, I would add drive 'a' 500gb to the mix by cloning the partitions and then adding as a spare.

So...does this sound like the way to upgrade from 250gb to 500gb drives on a raid 1 software raid?

Or, is it back to the drawing board?