DRBD 8.4.2 Has been Released
For any user of DRBD-8.4, we suggest an upgrade to 8.4.2 as changes to the kernel in version 2.6.36 or newer have caused an issue that may cause data corruption on a Secondary/Sync target when using protocols A or B. (In the 8.3 series this was already fixed with the 8.3.13 release).
It is worth noting that all previous DRBD releases did not enforce correct ordering of (some) write operations on a resync-target node. It is a rare condition that could trigger the potential data corruption. It may cause corruption in the sense that it looks like if a single block write was not executed on the secondary. Actually it was overwritten with the previous version of the data. This second write originates from the resync process.
Apart from that those nasty bugs, we have also fixed a condition where "disk-barrier no" and "disk-flushes no" were ineffective. This was the reason why some people were reporting "drbd-8.3 is faster than drbd-8.4".