Ric Wheeler wrote: > Hans Reiser wrote: >> I am skeptical that bitflip errors above the storage layer are as common >> as the ZFS authors say, and their statistics that I have seen somehow >> lack a lot of detail about how they were gathered. If, say, a device >> with 100 errors counts as 100 instances for their statistics..... Well, >> it would be nice to know how they were gathered. Next time I meet them >> I must ask. >> > I think that most big vendors have a lot of information about failure > rates on drives, but cannot actually share the details in public (due > to NDA's with the suppliers). > > One thing that we are trying to do is to get some of the more > "community" oriented people at Seagate Research to come out and talk > to the people about what are reasonable types of errors to code > against. Current idea is to get everyone in the same place a couple > of days before the next FAST conference (i.e., linux IO people or file > system people and these vendors). (See the USENIX page for details on > FAST at http://www.usenix.org/events/fast07/cfp/). > > I will say that media errors tend to be larger than single bit errors, > i.e. you will lose a set of sectors instead of seeing a single bit > flip on one sector (remember that the drive vendors do extensive ECC > at their level). What their ECC will not fix is something like junk > settling on the platter or a really bad error like a bad disk head. I think that integration of fs, fsck, and raid is the right solution for media errors. What I haven't seen data I trust on is what is bitflip error rate for the non-media sources. Since I haven't seen data I believe (where belief requires details being supplied), my inclination is to say plugins that users can choose to use if they want them are the right solution. > I think that ECC would be overkill, I view it as an option that we make available to enterprise customers who want to feel good.
It is not for me to tell them that they are wrong, for I lack the data, it is merely for me to supply it as a non-default option, and let the users tell me how often it actually gets triggered when they use it.
