I'm not doing this now, just "planning" per se but I currently have a RAID 5 array in a home server consisting of 4 x 2TB hard drives. I'm beginning the process of ripping all of my DVD's to this array and my DVD collection is large enough that I will end up filling up this 6TB array quite easily (8TB, 6TB available in RAID 5).
So, I'm wondering...when it comes time to double the capacity (and 4TB drives are more prominent/cheaper etc) could I just replace a single drive in the array with the larger drive, rebuild, then repeat until all four drives are replaced or would I still just end up with a 6TB array and half the drive space not used?
If I can do this and it would use all of the new space giving me 12TB availalbe, *in your opinion* would it be faster / more efficient to copy the data on the existing 6TB array off to external storage then just replace all drives and build a new array then copy back, or more efficient to do the single drive at a time swap?
My thinking is, it would probably be faster to copy off, replace the entire array, then copy back but seems to me that would be more overhead (my own time spent "working on it") then just doing a quick drive swap one day...two days later do another etc until done...Would take me all of 20 minutes of my time (over the course of a week or so)...Where as a copy, replace, copy back would take at LEAST a few hours of my time regularly checking in the copy, making sure everything made it in the copy(s) etc.
A lot of this probably depends on the features of your RAID controller.
Can you replace your 2TB disks one at a time with 4TB disks?
Yes, however, the RAID controller will most likely treat each disk as if it is the size of the smallest disk in the array. In your case, that's 2TB. Once you replace all your disks with 4TB disks you should be able to expand the array to fill the entire disk space (again, controller dependent). I believe this is the procedure you are describing and in theory it should work. The downside of this approach is that each time you replace a disk you'll have to do a rebuild which will take time and during that time your data is at risk.
So overall you'd be looking at 4 rebuilds (which can be very time consuming on 2TB disks) and an expansion to use all of the storage available on the 4TB disks once all the 2TB disks have been replaced (even LONGER than a rebuild on 2TB disks). Again, depending on your controller and disks, I could easily see this process taking weeks or months. During that time any error (by the controller, a power outage, a computer crash, a disk failure) and you could, and probably would, lose all your data.
It would be much easier, hugely quicker (thinks days instead of months), and safer to copy the data off the array of 2TB disks, take them out of the computer, put in the 4TB disks, build a new array, and then copy all the data back on. The beauty of this plan is that even if something screws up in the process, all the data is still on the 2TB disks and should theoretically be recoverable.
Thinking you're right...in looking at expansion options I was looking at the 12TB buffalo usb 3 external drive (pricey as hell, but...)...thinking maybe when it's time to expand I get one of those, RAID 5 it and move all the movie files to it... then when it's time to expand again move all data to it, replace the internal raid 5, move all data back then use the buffalo as a local backup.