Adding a new hard drive to RAID1 software RAID fails I've got a Mac Pro 1.1 running macOS Server 10.6.8 that I want to use as a RAID-Server. I use Disk Utility to run a RAID1 set with two 500GB hard drives.

Now adding a third 500GB hard drive to the existing RAID-Set with diskutil appleraid add member fails by showing me the following error message:

Error: -9911: The target disk appears to be too small to add to this RAID set

But when I delete the RAID-Set and set it up with all three hard drives together, the RAID is being created without any problem.

I belive that it could have something to do with the fact, that the third hard drive is a different model (different company), and the other two are the exact same. But if that would be the case, then I could not replace a hard drive in a RAID-Set, even if it would be from the same company and the same model line – since even those can change over time – except if I buy the exact same one – right?



I want to be sure that Apple RAID is capable of adding a new drive to an existing RAID if I have to swap a damaged one. Is anyone able to help me with this problem?

Thanks in advance!
I did not know, that it's not ok to cross post over multiple platforms – sorry for that.

However on superuser I got an answer to my problem, so here is the link once again:
https://superuser.com/questions/1476652/adding-a-new-hard-drive-to-raid1-software-raid-fails