On May 1, 2010, at 1:56 PM, Bob Friesenhahn wrote: > On Fri, 30 Apr 2010, Freddie Cash wrote: >> Without a periodic scrub that touches every single bit of data in the pool, >> how can you be sure >> that 10-year files that haven't been opened in 5 years are still intact? > > You don't. But it seems that having two or three extra copies of the data on > different disks should instill considerable confidence. With sufficient > redundancy, chances are that the computer will explode before it loses data > due to media corruption. The calculated time before data loss becomes longer > than even the pyramids in Egypt could withstand.
These calculations are based on fixed MTBF. But disk MTBF decreases with age. Most disks are only rated at 3-5 years of expected lifetime. Hence, archivists use solutions with longer lifetimes (high quality tape = 30 years) and plans for migrating the data to newer media before the expected media lifetime is reached. In short, if you don't expect to read your 5-year lifetime rated disk for another 5 years, then your solution is uhmm... shall we say... in need of improvement. > > The situation becomes similar to having a house with a heavy front door with > three deadbolt locks, and many glass windows. The front door with its three > locks is no longer a concern when you are evaluating your home for its > security against burglary or home invasion because the glass windows are so > fragile and easily broken. > > It is necessary to look at all the factors which might result in data loss > before deciding what the most effective steps are to minimize the probability > of loss. Yep... and manage the data over time. There is a good reason why library scientists will never worry about the future of their profession :-) http://en.wikipedia.org/wiki/Library_science -- richard ZFS storage and performance consulting at http://www.RichardElling.com _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
