ganeti: optimized DRBD parameters

diff --git a/input/howto/install-ganeti.creole b/input/howto/install-ganeti.creole
index e499613..2f21981 100644 (file)
--- a/input/howto/install-ganeti.creole
+++ b/input/howto/install-ganeti.creole
@@ -468,6 +468,21 @@ Order is important, or else things get very, very confused and the world needs a
   gnt-cluster command "echo 1 > /sys/bus/pci/devices/0000:0e:00.0/cciss0/rescan"
 }}}
 
+
+=== DRBD optimization ===
+
+The default DRBD parameters are not really optimized, which means very slow (re)syncing. The
+following commands might help to make it faster. Of course the max speed can be increased if
+both the network and disk speed allow that.
+
+{{{
+    gnt-cluster modify -D drbd:net-custom="--max-buffers 36k --sndbuf-size 1024k --rcvbuf-size 2048k"
+    gnt-cluster modify -D drbd:c-min-rate=32768
+    gnt-cluster modify -D drbd:c-max-rate=98304
+    gnt-cluster modify -D drbd:resync-rate=98304
+}}}
+
+
 === Change the CPU type ===
 
 Modern processors come with a wide variety of additional instruction sets (SSE, AES-NI, etc.) which vary from processor to processor, but can greatly improve the performance depending on the workload. Ganeti and QEMU default to a compatible subset of cpu features called qemu64, so that if the host processor is changed, or a live migration is performed, the guest will see its CPUfeatures unchanged. This is great for compatibility but comes at a performance cost.