public java.lang.String getSourceDisk() {
      java.lang.Object ref = sourceDisk_;
      if (!(ref instanceof java.lang.String)) {
        com.google.protobuf.ByteString bs = (com.google.protobuf.ByteString) ref;
        java.lang.String s = bs.toStringUtf8();
        sourceDisk_ = s;
        return s;
      } else {
        return (java.lang.String) ref;
      }
    }
<pre>
Specifies the full path to an existing disk.
For example: "projects/my-project/zones/us-central1-c/disks/my-disk".
</pre>

<code>string source_disk = 3;</code>

@return The sourceDisk.
java-tpu/proto-google-cloud-tpu-v2alpha1/src/main/java/com/google/cloud/tpu/v2alpha1/AttachedDisk.java