X-Git-Url: https://git.adam-barratt.org.uk/?a=blobdiff_plain;f=input%2Fhowto%2Finstall-ganeti.creole;h=d88f02401053b5693d42b1b42419e7210a6bd7d0;hb=4748598a49ca95a8569fb7638db087e00821ddeb;hp=e4996132fdfead62a9f3220493204adada8bfe38;hpb=f4ea7e28a138227dfa183ab828c3ae5a2e0a9001;p=mirror%2Fdsa-wiki.git

diff --git a/input/howto/install-ganeti.creole b/input/howto/install-ganeti.creole
index e499613..d88f024 100644
--- a/input/howto/install-ganeti.creole
+++ b/input/howto/install-ganeti.creole
@@ -468,6 +468,31 @@ 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 disk cache ===
+
+When using raw volumes or partitions, it is best to avoid the host cache completely to reduce data copies
+and bus traffic. This can be done using:
+
+{{{
+    gnt-cluster modify -H kvm:disk_cache=none
+}}}
+
+
 === 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.