You did, but there were read errors on disk1 during the sync, so parity isn't 100% valid, you can still rebuild but there will likely be some data corruption, except if you are very lucky and the read errors coincided with empty disk space, or use ddrescue, this way you can at least now with files are corrupt, another alternative is to copy the data form disk1 to another disk, any files that you can't copy need to be restored from backups.