Thank you so much Jorge, I wasn't sure I should restart before I got advice in case you needed extra logs etc. But that did the trick.
Is there any easy way for a noob like me to know when I should and shouldn't try a reboot, in case I encounter an error like this again?
Also, is it advisable to use unbalance, to move data off disks before replacing them with larger disks?
Thanks so much again, for sorting me out so quickly