Accidentally used dd on my system drive As is wanted to write an image to usb stick, I accidentally used my system drive (macintosh hd) as target. Command used:

sudo dd if=/dev/zero of=/dev/rdisk1 bs=1024 count=1


Where disk1 was Macinstosh HD ... (yeah I know - facepalm :)

Anyway - aborted after 2 minutes as nothing happened and I realised my mistake. To my astonishment, everything still seems to work, partition still there, still reboots.

This is the output of: 

$diskutil list:

/dev/disk0
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *500.3 GB   disk0
   1:                        EFI EFI                     209.7 MB   disk0s1
   2:          Apple_CoreStorage                         499.4 GB   disk0s2
   3:                 Apple_Boot Recovery HD             650.0 MB   disk0s3
/dev/disk1
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:                  Apple_HFS Macintosh HD           *499.1 GB   disk1
                                 Logical Volume on disk0s2


The command was intented to zero out the partion map (of an usb stick) ...as described here.

Which works on the usb stick, (luckily) it didn't work on my Macintosh hard disc. But i still don't get it why? By saying i aborted i meant after committing the comment, nothing happened, not output, but no fresh prompt either..so is used ctrl-c

Time machine backups can be restored, thats not the thing. I'm just curious and want to understand it

Do I still have to worry that I lost some data?
Your main disk uses a Core Storage partition scheme:

disk0 is your main system disk.
disk1 is a &quot;virtual&quot; disk residing in disk0s2 containing the Macintosh HD volume visible on your desktop.

The first two sectors of a Logical Volume contain zeros only.
Examples:

disk2 is the Core Storage Volume pooling disk0s2 (SSD) and disk1s2 (HDD) of a 3.1 TB Fusion Drive


disk2 is the Core Storage Volume residing in disk0 - the 64 GB disk image of a Parallels VM (Yosemite)



With your command sudo dd if=/dev/zero of=/dev/rdisk1 bs=1024 count=1 you had luck and you just have overwritten 1024 zeros with 1024 zeros.
As a result you haven't lost any data and may continue working with your Mac without the need to restore any backup or to reinstall your system.