2 new HDD. Full expansion of RAID set (all at once, one at a time), or save a drive for a rainy day

Looking for input. I have 6x3TB RAID-6. I have 2 new 3TB drives coming in next week. I see the following options.

1 - Install them both at the same time, grow the array to 18TB. Probably slower expand/rebuild time, only one rebuild.
2 - Install them one at a time, grow the array to 15, then 18TB. Might be marginally faster, extra drive in case rebuild fails on first go, two expand/rebuild processes.
3 - Install a single drive, expand to 15TB. Save the 3rd for when a drive decides to go belly up (or install it and mark it as a backup/recovery/whatever drive).

Currently I'm at ~92% full on the array. Using about 65-70GB per month, so one additional 3TB drive should last me more than a year at this point before I need to grow/expand again.

I hate the expansion/rebuild process, I get so paranoid all that writing is going to kill a drive. Thoughts, suggestions? WWOMVD?

Thanks!

Thanks for the input! Sounds like solid advice. Any benefit to leaving it cold (just in a box on the shelf), vs hooking it up and marking it as a spare? I can't seem to find the option in the UI now, but I thought before you add the device to the array you could mark is as a stand-by / spare disk in case the array degraded and needed to use it.. maybe I just dreamt that up.

Zitat von davidh2k

Cold spare may live longer vs. hot-spare jumps in the exact moment one drive dies.

Your decision.

Greetings
David

Thanks again! Final decision was to order 3 drives.. expand the array with 2 drives to hold me over for the next couple of years. One drive will be cold spare. That's it for this array, no more expansion.

I think by the time I fill up the remaining 6TB, I should be planning a complete replacement of the array anyway (hopefully with 6TB or even 10TB drives by 2016).

12.5 hours down, ~25 more to go. ::fingers crossed::