That doesn't mean anything. Drives can fail at random times, even if they are the exact same drives in the exact same machine. The slave or master setting only tells the computer BIOS which drive is the primary boot drive that holds the O.S kernel to boot too. Both drives are still spinning at 7200rpm even if there is no data writing/scanning on the slave in comparison to the master unless there you enabled a power saving shut down feature. In any case,such is the tradeoff for magnetic storage media, there just not horrendously reliable after a few years of use. SSD's will be the future of data storage in the coming years.