On Sun, May 2, 2010 14:12, Richard Elling wrote: > 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.
Are they giving tape that long an estimated life these days? They certainly weren't last time I looked. And I basically don't trust tape; too many bad experiences (ever since I moved off of DECTape, I've been having bad experiences with tape). The drives are terribly expensive and I can't afford redundancy, and in thirty years I very probably could not buy a new drive for my old tapes. I started out a big fan of tape, but the economics have been very much against it in the range I'm working (small; 1.2 terabytes usable on my server currently). I don't expect I'll keep my hard disks for 30 years; I expect I'll upgrade them periodically, probably even within their MTBF. (Although note that, though tests haven't been run, the MTBF of a 5-year disk after 4 years is nearly certainly greater than 1 year.) -- David Dyer-Bennet, d...@dd-b.net; http://dd-b.net/ Snapshots: http://dd-b.net/dd-b/SnapshotAlbum/data/ Photos: http://dd-b.net/photography/gallery/ Dragaera: http://dragaera.info _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
