Finally ext4 ...or not?

I bought a new HDD and set up RAID 1 with LVM and ext4. (I made it using mkfs.ext4) I was just about to rm my backups I stored on my other disks when rsync failed and I wasn't able to access my new partition anymore. Everything threw I/O Errors.
I wanted to run fsck, but I told me the disk was in use (it wasn't). Couldn't figure out what was the problem so I rebooted and got an error, telling that mount can't mount the partition because it's not ext4 (as I specified in /etc/fstab).
Well I started fsck.ext4 and it threw quite a lot of errors and after some time it started to loop.

Restarting e2fsck from the beginning...
/dev/mapper/VolGroup00-data contains a file system with errors, check forced.
Pass 1: Checking inodes, blocks, and sizes
Root inode is not a directory.  Clear? yes

Inode 5 has illegal block(s).  Clear? yes

Illegal block #12738657 (1613830228) in inode 5.  CLEARED.
Illegal block #12738658 (3211906433) in inode 5.  CLEARED.
Illegal block #12738659 (478689490) in inode 5.  CLEARED.
Illegal block #12738660 (3876020224) in inode 5.  CLEARED.
Illegal block #12738661 (1007945148) in inode 5.  CLEARED.
Illegal block #12738662 (1205590462) in inode 5.  CLEARED.
Illegal block #12738663 (3567108197) in inode 5.  CLEARED.
Illegal block #12738664 (3575479245) in inode 5.  CLEARED.
Illegal block #12738665 (2383729051) in inode 5.  CLEARED.
Illegal block #12738666 (619555458) in inode 5.  CLEARED.
Illegal block #12738667 (3902957544) in inode 5.  CLEARED.
Too many illegal blocks in inode 5.
Clear inode? yes

Restarting e2fsck from the beginning...
/dev/mapper/VolGroup00-data contains a file system with errors, check forced.
Pass 1: Checking inodes, blocks, and sizes
Root inode is not a directory.  Clear? yes

Inode 5 has illegal block(s).  Clear? yes

Illegal block #12738668 (1246693144) in inode 5.  CLEARED.
Illegal block #12738669 (2312789758) in inode 5.  CLEARED.
Illegal block #12738670 (332492032) in inode 5.  CLEARED.
Illegal block #12738671 (3850324777) in inode 5.  CLEARED.
Illegal block #12738672 (2442788202) in inode 5.  CLEARED.
Illegal block #12738673 (4227858239) in inode 5.  CLEARED.
Illegal block #12738676 (311437445) in inode 5.  CLEARED.
Illegal block #12738677 (4016009761) in inode 5.  CLEARED.
Illegal block #12738678 (3776456913) in inode 5.  CLEARED.
Illegal block #12738679 (528482688) in inode 5.  CLEARED.
Illegal block #12738680 (1343549598) in inode 5.  CLEARED.
Too many illegal blocks in inode 5.
Clear inode? yes

Now I knew my FS actually died :( I was maybe 3h old.

Here's the command that killed it:
rsync -rvtlpEog --safe-links ~/backup/mistral_backup/ mistral_backup/ --progress

To all ext4 users: Make backups on some different FS! Ext4 is NOT stable!

Update:
The problem could be that I didn't wait for the RAID to finish syncing.