[GLLUG] Advice on expanding an existing RAID 1 installation

[John Winters]

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.

TIA,
John