Did you notice what kind of speeds the parity check indicated after it crossed the 4TB point?  (i.e. when it gets to the point where the only drives involved in the check are the 2 6TB drives, but before it gets too close to the inner cylinders of those drives)

 

With the 1.2TB/platter areal density, I'd expect some very nice speeds at that point.  [it'd be really nice to know what they'd be on the outermost cylinders, but there's no way to know that since they're already in your array.]

 

 

Hi, I'm doing disk upgrades and necessary parity/data-rebuilds atm.

 

Speed during the rebuild of my disk1 went from 83 MB/s (Seagate 4TB) right before the 4TB mark up to 132 MB/s at 4.02 TB (WD60EFRX) according to the web frontend.

 

The complete 6TB parity rebuild the day before took about 16 hours on a mixed array of 2, 4 and 6TB drives.

Thanks for the feedback.  That's a nice jump in speed once your array hits the point where only the 6TB units are involved.