Converting single non-raid to raid1

[dsr-mzpnVDyJpH4k7aNtvndDlA at public.gmane.org (Dan Ritter)]

On Wed, Feb 17, 2010 at 11:06:04AM -0500, Jerry Feldman wrote:
> With large drives currently at low prices, I am considering buying a
> second 1TB drive and setting up a S/W raid1. The procedure is pretty
> straightforward by setting up the new drive as a single volume raid1,
> then set up LVM with roughly the same sizes, and copy the data to the
> new raid1 volume, set up GRUB...
> 
> Does the new physical drive need to be the same geometry as the older
> drive. Let's say I have a Seagate 1TB, and buy a new WD 1TB drive, will
> that cause a problem as long as the raid partition on both are the same
> size.

They do not need to be the same geometry. If the interfaces are
of grossly mismatching speed (say, USB2 vs PATA), you will run
into frequent resynch issues.

> Secondly, is there any advantage or disadvantage to allocating the boot
> partition as a raid1. I think in a prior discussion, there was an
> overwhelming opinion that swap should be on the raid1.

I sometimes prefer to have separate boot partitions on each disk
which are not RAIDed together. That incurs the cost of manually
keeping them up to date, but provides the benefit of not wiping
out both of them with a single filesystem event.

-dsr-