direct links of old sources may well be a few messages off.
To recap the benchmark tests... two identical servers (hardware and software) /dev/sdb is a single 36G 15K U160 scsi seagate kernel-18.104.22.168 with drbd-8.0.1 [drbd module NOT loaded] ./dm -a 0 -b 1M -s 3G -y -m -p -o /dev/sdb ... [ multiple concurrent tests yield ~70 MB/sec ] [modprobe drbd (no ps running, not started, just loaded)] ./dm -a 0 -b 1M -s 3G -y -m -p -o /dev/sdb ... [ multiple concurrent tests yield ~70 MB/sec ] so far, so good.... [drbdadm adjust all] (worker thread started) (drbd in "st:Secondary/Unknown" "ds:UpToDate/DUnknown" state) ./dm -a 0 -b 1M -s 3G -y -m -p -o /dev/sdb ... [ multiple concurrent tests yeild ... ~70 MB/sec initially and degrades with each additional passing of the benchmark. After 2 tests, performance is down to 50 - 60 MB/sec. After 10 tests performance is down to < 30 MB/sec. After 20 tests performance is down to < 25 MB/sec. [drbdadm disconnnect all] (acutally not needed, in disconnected state already) No change, performance has not changed. Still degraded to ~ 25 MB/sec. [drbdadm detach all] (worker thread killed) (module still loaded) BIG change!!! Benchmark now up to ~70 MB/sec !!! Tests conduced on two identical machines, both provided identical back-to-back results.