Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.
Lars, first of all, thanks a _lot_ for this detailed explanation! I guess this post will help many people in the future. Could you add the warning about false positives to the Users Guide at http://www.drbd.org/users-guide/s-integrity-check.html too? > Quoting the DRBD User's Guide: > Notes on data integrity > > This may happen for swap, or for certain append while global sync, or > truncate/rewrite workloads, and not necessarily poses a problem for the > integrity of the data. Usually when the initiator of the data transfer > does this, it already knows that that data block will not be part of an > on disk data structure, or will be resubmitted with correct data soon > enough. This is new in drbd.conf(5) of 8.3.10. Unfortunately I was only aware of 8.3.9 which just mentions swap and ReiserFS. Having neither of those two, I thought I was "free" of false positives... > If you want to have DRBD do "end-to-end" data checksums, even if the > data buffers may be modified while being in flight, and still want it to > be efficient, sponsor feature development. Fair enough! ;-) > The Problem: > http://lwn.net/Articles/429305/ > http://thread.gmane.org/gmane.linux.kernel/1103571 > http://thread.gmane.org/gmane.linux.scsi/59259 > > And many many more older threads on various ML, > some of them misleading, some of them mixing > this issue of in-flight modifications > with actual (hardware caused) data corruption. This and the (outdated) notes of drbd.conf(5) probably got me on the "wrong" track. It also explains why I was unable to reproduce any data corruption. > Possible Solutions: [...] One last question for clarification, though: Given the above, even online verify isn't free of false positives, right? Then some out-of-sync blocks are to be expected. If so, a warning in the manpage and guide too would probably avoid some gray hair. ;-) Thanks again and best regards, Walter -- GMX DSL Doppel-Flat ab 19,99 Euro/mtl.! Jetzt mit gratis Handy-Flat! http://portal.gmx.net/de/go/dsl