Time machine is a big risk to your data if you trust its reliability. I just seem to have lost the backup from 4 Month worth of data (3TB) and it's not the first time that TM malfunctions. I had no crash, nothing happening, running my MacPro just besides me working on an MBA. Then, this afternoon I noticed audible and hours long disk activity. TM's icon indicated backup activity. When checking the backup volume TM was just running something like a first backup on my 2.3 TB HDD. No older backup was preserved. Fortunately I still have a daily backup on an external device and a weekly backup separately, but my WARNING TO EVERYBODY: NEVER EVER TRUST TIME MACHINE (so-called) BACKUPS. They are prone to vanish without warning and cannot be relied on. YOU NEED AT LEAST ONE OTHER BACKUP DONE BY ANOTHER APPLICATION. Using another application is absolutely crucial. I use Chronosync and CarbonCopyCloner.