Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.
> > 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. ;-) > > Uhm. Well. > Online verify does _not_ suffer from _this_ problem. Ok. Problem is, the weekly verify usually sees several (about 20-30 for a 700 GiB drbd device) blocks out-of-sync. > The pages used to read in and compare data are private to DRBD in this > case, and we won't modify them while we are calculating checksums. > Application IO is locked out while we are reading the data for checksums. > > So if DRBD Online Verify finds out-of-sync blocks, > they have been out of sync at that point in time. > > They may be unlucky enough to see blocks where data has been modified in > flight, and as a result local and remote disk contain differing blocks. So, not necessarily _this_ problem but a similar one... > Such differences should be very short lived, though, > as modification means re-dirtying, and that means > the page will be resubmitted by upper layers "soon". > > Unless these block belong to files that are unlinked before the > respective re-dirtied page is written out again (and thus the > re-dirtied page is simply discarded, before being re-submitted). Hence swap is listed first in the man-page. Databases are probably also more likely for causing this, right? > Conclusion: > out-of-sync blocks found by online verify, or software raid1 > "resilvering", any similar procedures, do not necessarily mean > broken hardware or memory corruption. The conclusion from the user perspective then is: Verify must not find any out-of-sync blocks _only_ if everything on top of drbd is idle (i.e. read-only or unmounted). Lars, thanks again to clarify this issue! IMHO you should add this to the documentation of the data integrity section. Best regards, Walter -- GMX DSL Doppel-Flat ab 19,99 Euro/mtl.! Jetzt mit gratis Handy-Flat! http://portal.gmx.net/de/go/dsl