David Magda wrote:
On Jul 12, 2006, at 20:10, Richard Elling wrote:G1. for 3 <= Ndisks <=5, RAID-Z2 offers the best resiliency/space. For Ndisks > 5, RAID-1 offers best resiliency/space. Ndisk-way RAID-1 always wins the resiliency, availability, and MTTDL but most people won't do it for Ndisks > 2.Can you give some numeric examples for one or two cases? I'm having troubling 'visualizing' why this would be the case (especially for N > 5).
For a binary resiliency analysis, 8 disks -> 2^8 possible working/failed states. Of those, a RAID-1+0 zpool will survive in 31.6% of the states versus only 14.5% for raidz2. This is a mathematical description of the sometimes more intuitive (sometimes not so intuitive) notion that the raidz2 zpool can survive if any 2 disks fail, whereas the RAID-1+0 zpool can survive up to 4 failed disks, as long as the failed disks are not in a single mirrored pair. Such analysis has nothing to do with availability, it is just a point-in-time assessment of resiliency. -- richard _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
