Erase and overwrite Disk on Synology DiskStation

I wanted to erase and overwrite the data on some hard disks that I need to downgrade my RAID 5 from three 4TB WD Red to only two. The erase function on the webgui doesn't work - something message like "don't possible with your drive". I search and found an alternative:

dd if=/dev/zero of=/dev/sdX bs=1M conv=noerror

To identify the disk use fdisk and/or hdparm:

fdisk -l
hdparm -I /dev/sdX

To run the dd command furthermore after disconnection from the SSH connection, use nohup:

nohup dd if=/dev/zero of=/dev/sdX bs=1M conv=noerror

Add a physical disk to VMware Fusion

1. Get Disk-ID from Disk ("disk1" in my case)
2. Open Terminal
3.Change current directory to:


4. Run vmware-rawdiskCreator with the right disk. This will create a new external-hdd.vmdk file in your home folder:

./vmware-rawdiskCreator create /dev/disk1 fullDevice ~/external-hdd ide

5. Open Vm Config file (*.vmx) with TextEdit and add following lines:

ide1:1.present = "TRUE"
ide1:1.fileName = "external-hdd.vmdk"

6. save and quit