Hi, On Monday 12 October 2009 19:44:47 Jörn Nettingsmeier wrote: > Arnold Krille wrote: > > Unless I miss something on AVLinux: > > On Saturday 03 October 2009 21:36:54 Jörn Nettingsmeier wrote: > >> Jonathan E. Brickman wrote: > >>>> You should at least use RAID6. > >>> 1. How does RAID6 differ from RAID5? > >> raid 6 uses a more elaborate algorithm than the simple parity of raid5, > >> to calculate two redundant bits. so you can recover from the failure of > >> two disks out of a raid6 array. > > > > Loosing two disks means you got more then two coupled. If so, you have > > definitely several of the same charge in that array. (Don't deny it, the > > human laziness speaks against you.) > > Recovering will still do heavy load on the disks. Now calculate the > > probability of two disks of the same charge failing without a third disk > > of that charge failing during recovery. Pretty low, huh? > that remark is bogus. each disk design has a mean-time between failures > of X hours. that means of N disks, N/2 will have failed after time X for > a sufficiently high number of samples N. > the failure of each individual disk is a statistically independent > event. Please listen to what I said: Two (or more) disks of the same manufacturer and same type and maybe even continuous id-numbers. And, bang!, now the failure of one device is highly connected to the failure of the other one. Because the error (or call it small mis-fit) happening in the production of the first is repeated in the second with a high probability. And I worked on a manufacturing band several times, I know how humans catch slight errors only after doing them the third or fourth time. By which its too late to sort out and check the last three products. > there is absolutely no synchronized self-destruct of disks > belonging to the same batch. Yes, there is! I know from bad experience, both my own (not very tragic) and that of a big company. Have fun and make backups, Arnold
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