Hi,

I currently have 3 drives in my array (8 TB (parity), 6 TB and a 3 TB (both data)).

I have bought 5 new and larger disks so I will be changing all of them.

How do I do it the right way when all should be exchanged?

Personally, I would run a non-correcting parity check first to verify that all of the disks can be currently read.  

 

If that runs without an error, I would replace the parity disk and add the two new data disks.   After parity rebuild and the formatting and clearing of the new disks, I would use the newly configured server for a month.  This will verify that there are no infant mortality problems with the new disks.  (You want to do this before the vendors return window expires!  In fact, I would run another non-correcting parity check just before expiration....)

 

Then replace one of the old data disks.  Replace the second disk after a couple of weeks.  (Store the old data disks for at least month after that.  They are an emergency backup of your data!)

 

(I am a bit paranoid and take more caution than many folks do but I worked in my prior life as a engineer and got my fingers burnt a few too many times when it was assumed that everything would go smoothly!  In fact, one of things that I learned is that, if you planned for things not to go smoothly, any problems encountered were more easily corrected.)