LVM + RAID follow up

[john.abreau at zuken.com (John Abreau)]

On Tue, 2006-11-07 at 15:32 -0500, Derek Atkins wrote:

> 
> Do you?  If I assume that the RAID5 is all one partition, then if the
> partition size increases I can just run resize2fs to increase the size
> of the file system.  The only question is the RAID5 parts, will it
> be able to build a filesystem out of a 3x400GB + 3x800GB partition?

You could try to do everything at the RAID level, but that seems 
more complicated and error-prone. I don't know if you can mix 
volumes of different sizes within a RAID device; I doubt it, and 
if it is possible, I imagine it would be messy. 

At the LVM level, you have a Volume Group (VG) which is comparable 
to a RAID metadevice; it's made up of one or more Physical Volumes 
(PV), each of which could be a single disk or a RAID set. The PVs 
can be of different sizes, which takes care of the upgrade path. 

If you're replacing an old disk, you can add the new disk, move 
the contents of the old disk to the new one, and remove the old 
disk from the VG, in a few simple steps:

    # Add a new RAID device /dev/md4
    vgextend FooVG /dev/md4

    # Move everything from /dev/md2 to /dev/md4
    pvmove -v /dev/md2 /dev/md4

    # Remove /dev/md2 from the VG
    vgreduce FooVG /dev/md2


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