Darren Dunham wrote: >> While its true that RAIDZ2 is /much /safer that RAIDZ, it seems that >> /any /RAIDZ configuration will outlive me and so I conclude that RAIDZ2 >> is unnecessary in a practical sense... This conclusion surprises me >> given the amount of attention people give to double-parity solutions - >> what am I overlooking? >> > > When talking to Netapp, some of their folks have mentioned their DP > solution wasn't necessarily so useful for handling near-simultaneous > disk loss (although it does do that). > > But that when a disk failed, it would not be uncommon for reconstruction > to be unable to read some data off the remaining disks (perhaps a bad > sector or bad data that fails checksum). With 1P, you have to shut down > the volume or leave a hole in the filesystem. With 2P, you reconstruct > that one read and continue. > > Are Netapp using some kind of block checksumming? That seems to be one of the big wins of ZFS compared to ordinary filesystems -- I have a higher confidence that data I haven't accessed recently is still good. If Netapp doesn't do something like that, that would explain why there's frequently trouble reconstructing, and point up a major ZFS advantage.
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