ps 6000 automatically expansion

Dear all,

I have a ps6000 storage. I had 12 X SAS 300GB HDD's in Raid 5 configuration with one hot-spare. Recently i decided to add 4 more identical HDD,s.I installed the HDD's on the 4 remaining bays and i left server room, after a couple of hours when i returned back i noticed that one of the existing HDD's has failed. I thought OK i will take one of the 4 new HDD's and replace it with that ,so i did and i left server room. When i returned to my office that is in another town i logged in the PS6000 management and then i realized that when i installed the 4 x HDD the array automatically was expanded without asking me(i have experience with HP and IBM storage and i never have seen that before). Also i noticed that the HDD that i used to replaced the failed disk was already member of the array and an automatically reconstruction was started. Anyway, now after reconstruction my array raid5 is healthy but there is a warning that a hot-spare is missing. My question is if i buy new disk what will happen? Will again automatically expand the array,will be automatically configured as a hot spare, or will do nothing?

Regards

Pantos