I've been running a WB 1TB MyStudio FW800 drive as for Time Machine back-up for a year or so. I had it set up as two partitions. A few weeks ago one the partition used for Time Machine stopped working. A verify revealed an Invalid Node Structure error. I reformatted the disk, overwriting with zeros, as a single partition and it checked out OK and ran OK for a couple weeks. But now I'm getting the same Invalid Node Structure error. Is it time to bite the bullet and replace it?