In a former life I ran a web site with a co-founder. We needed to upgrade our main system (we only had 2), and had mirrored RAID1 hard drives, some backup but not great. We tested the new system, it appeared to work fine, so the plan was to take it to the colo, rsync the old system to the new one, make sure everything ran okay, then bring the old system home.
We did the rsync, started the new system, it seemed to be working okay, but then we started seeing some weird errors. After some investigation, it looked like the rsync didn't work right. We were tired, it was getting late, so we decided to put one of the original mirrors in the new system since we knew it worked.
Started up the new system with the old mirror, it ran for a while, then started acted weird too. At that point we only had 1 mirror left, were beat, and decided to pack the old and new system up and bring it all back to the office (my co-founder's house!) and figure out what was going on. We couldn't afford to lose the last mirror.
After making another mirror in the old system, we started testing the new system. It seemed to work fine with 1 disk in either bay (it had 2). But when we put them in together and started doing I/O from A to B, it corrupted drive A. We weren't even writing to drive A!
For the next test, I put both drives on 1 IDE controller instead of each on its own controller. (Motherboards had 2 IDE controllers, each supported 2 drives). That worked fine.
It turns out there was a defect on the MB and if both IDE ports were active, it got confused and sent data to the wrong drive. We needed the CPU upgrade so ended up running both drives on 1 IDE port and it worked fine until we replaced it a year later.
But we learned a valuable lesson: never ever use your production data when doing any kind of upgrade. Make copies, trash them, but don't use the originals. I think that lesson applies to the idea of doing an inplace conversion from NTFS to Btrfs, even if it says it keeps a backup. Do yourself a favor and copy the whole drive first, then mess around with the copy.
We did the rsync, started the new system, it seemed to be working okay, but then we started seeing some weird errors. After some investigation, it looked like the rsync didn't work right. We were tired, it was getting late, so we decided to put one of the original mirrors in the new system since we knew it worked.
Started up the new system with the old mirror, it ran for a while, then started acted weird too. At that point we only had 1 mirror left, were beat, and decided to pack the old and new system up and bring it all back to the office (my co-founder's house!) and figure out what was going on. We couldn't afford to lose the last mirror.
After making another mirror in the old system, we started testing the new system. It seemed to work fine with 1 disk in either bay (it had 2). But when we put them in together and started doing I/O from A to B, it corrupted drive A. We weren't even writing to drive A!
For the next test, I put both drives on 1 IDE controller instead of each on its own controller. (Motherboards had 2 IDE controllers, each supported 2 drives). That worked fine.
It turns out there was a defect on the MB and if both IDE ports were active, it got confused and sent data to the wrong drive. We needed the CPU upgrade so ended up running both drives on 1 IDE port and it worked fine until we replaced it a year later.
But we learned a valuable lesson: never ever use your production data when doing any kind of upgrade. Make copies, trash them, but don't use the originals. I think that lesson applies to the idea of doing an inplace conversion from NTFS to Btrfs, even if it says it keeps a backup. Do yourself a favor and copy the whole drive first, then mess around with the copy.