I have 6x3TB (5 data) disks array which I want to replace with 4x6TB (yes 3TB gain, but eventually I'll be adding more 6TBs).

From duration point of view, I'm pondering between

a) 1x1 replacement procedure (redundancy preserved)

Requires rebuilding 5x6TB for approx total 5x12 hours = 60hrs

 

vs

 

b) new config from the scratch (redundancy-voided) followed by manual copy of each original drive (using rsync).

Requires copying 5x3TB for approx total 5x6 hours = 30hrs.

Shorter time and probably benefit from the resulting defrag-ed state?

 

Edited October 12, 20187 yr by ldrax

or c)  redundancy replacing x4 and then copying 3TBx2 from the remaining 2 drives?  I'd go for that approach as you'll only be moving 6TB

Or

 

Add one more parity, then you may replace 2 disk each time.