Theoretical question about replacing a disk with a higher capacity one

[fitbrit]

Let's say parity is 6TB, and you're replacing a 3TB array disk with a 6 TB drive. I am currently in the process of doing this for many 3TB drives.

 

In theory, during the data rebuild, couldn't the last 3 TB on the 6 TB drive just be written with Zeros, after the first 3Tb of data has been rebuilt? That would certainly use less power, cause less stress on the drives and be faster, no?

[JorgeB]

It will right zeros, but there's no difference in power, stress or speed in writing zeros as opposed to any other data.

[fitbrit]

But it doesn't do that. Right now, I can see that it's reading parity and ALL my other disks to write to the new disk. It is writing all zeros if my parity was correct, but it's calculating this decision on the fly. If it knew to just write all zeros, regardless of what's on the other disks, it would only be writing to the one drive, and NOT reaidng from all the others. Hence lower, power, heat and duration to do so. I know my system writes zeros at about 100 MB/s, but the fastest my data is rebuilt is at 50-60 MB/s between 4-6TB. It starts off at ~35 MB/s until 3TB, and then goes up to ~$2 MB/s until 4 TB.