Bob Friesenhahn wrote: > On Thu, 8 May 2008, Ross wrote: > > >> protected even if a disk fails. I found this post quite an >> interesting >> read:http://blogs.sun.com/relling/entry/raid_recommendations_space_vs_mttdl >> > > Richard's blog entry does not tell the whole story. ZFS does not > protect against memory corruption errors and CPU execution errors > except for in the validated data path. It also does not protect you > against kernel bugs, corrosion, meteorite strikes, or civil unrest. > As a result, the MTTDL plots (which only consider media reliability > and redundancy) become quite incorrect as they reach stratospheric > levels. >
These are statistical models, or as they say, "every child in Lake Woebegon is above average." :-) The important take-away is that no protection sucks, single parity protection is better, and double parity protection is even better. See also the discussion on "mean time" measurements and when we don't like them at http://blogs.sun.com/relling/entry/using_mtbf_and_time_dependent -- richard > Note that Richard does include a critical disclaimer: "The MTTDL > calculation is one attribute of Reliability, Availability, and > Serviceability (RAS) which we can also calculate relatively easily." > Notice the operative word "one". > > The law of diminishing returns still applies. > > Bob > ====================================== > Bob Friesenhahn > [EMAIL PROTECTED], http://www.simplesystems.org/users/bfriesen/ > GraphicsMagick Maintainer, http://www.GraphicsMagick.org/ > > _______________________________________________ > zfs-discuss mailing list > zfs-discuss@opensolaris.org > http://mail.opensolaris.org/mailman/listinfo/zfs-discuss > _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
