[GLLUG] Advice on expanding an existing RAID 1 installation

[James Courtier-Dutton]

On 24 May 2014 11:12, John Winters <john at sinodun.org.uk> wrote:
> Dear GLLUGers,
>
> I seek a spot of advice on enhancing an existing RAID 1 installation (used
> for backing up all sorts of systems).
>
> The current system has 2 x 1TB drives in a RAID 1 configuration.  These are
> running out of space.
>
> I intend to get 3 x 3TB drives and would like to transfer everything to
> those.
>
> The Linux RAID Wiki has a page on extending an existing RAID array, but says
> I should start by removing one of my existing drives.  Presumably this isn't
> necessary if I have a spare physical slot/controller slot/power lead?
> Rather than their proposed approach of remove=>add=>remove=>add, is there
> any reason I can't do add=>remove=>add=>remove?
>
> Second question - I'm undecided about whether to put the 3rd drive into the
> system to start with (thus three drives up to date all the time) or keep it
> on a shelf for when it's needed.  Does anyone have strong views on which is
> better?
>
> The machine in question is only switched on for a couple of hours each day.
> It switches itself on, backs up a selection of other systems, then switches
> itself off again.
>

One other think to maybe consider is to not use RAID at all, and
instead use the features of the filesystem btrfs.
It has options for striping and doing RAID like features, with the
added benefit of you being able to arbitrarily add HDDs and it will
balance the data so that it is always contained on at least N physical
devices.

Kind Regards

James