Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.
Hi folks I need a bit of help understanding an issue we're seeing with our DRBD setup. We have two Debian systems, with DRBD 8.3.8. We have a resource configured with protocol A, which backs onto a single SATA disk on each side. I am running the latency test from the DRBD documentation, multiple times: while true; do dd if=/dev/zero of=$TEST_DEVICE bs=512 count=1000 oflag=direct; sync; done If I stop drbd and run it against the backing device on each side, it repeats again and again very quickly. If I start DRBD and run it against the DRBD device on the primary side, it runs quickly for about 4 or 5 repetitions, then slows right down. Investigation shows pe: is climbing in /proc/drbd, and iostat -mxd 1 on the secondary node shows 100% disk usage for the backing device. Note that this repeats in the other direction if I swap primary/secondary roles. It's only the secondary role that's seeing 100% disk usage, not the primary. When I use no-disk-barrier and no-disk-flushes, the problem goes away entirely - but I'm reluctant to enable this permanently, as they're just normal SATA drives without any battery backup or anything, and there are scary warnings about doing that in the documentation :-) Can someone recommend the appropriate action I should take to improve my performance please? Let me know if more information or debugging would be helpful. Thanks! Phil