I am currently running unRIAD 6.1.9 and am highly looking forward to the 6.2 release. I am looking to purchase a second parity drive in preparation for this release. My question is, can someone please explain how dual parity will expect read and write speeds to the array? Also, does anyone have any real numbers showing the performance of drives with different speeds in dual parity?

 

My HGST 4TB NAS drive reads and writes at 180MB/s. If I were to get a slower drive that does say 150MB/s read and write, will this reduce my overall read and write speed to the array?

It won't make any difference in read speeds, as only the actual data disk will be used, as for write speed dual parity in itself does not slowdown writes, unless you're using a 10 year old celeron, but if you're parity2 is considerably slower than parity, writes will be limited by the slower of the two, e.g:

 

You have only recent 7200 rpm disks as parity and data, say your current write speed (without turbo write) is ~75Mb/s, you add a recent 5400rpm disks as parity2, your write speed is going to decrease to ~60Mb/s.

Realistically you'll likely not notice any difference, although as Johnnie noted if your 2nd parity drive is slower than your first parity drive you may notice a small decrease in write speeds UNLESS you're using a cache, in which case you probably won't notice any difference at all.

 

Reads are impacted at all.

 

FWIW, when I upgraded my test server to dual parity, the total parity check time was almost identical to what it had been on 6.1.9, and I've noticed NO difference in overall performance.