Ubuntu Server mdadm drbd ocfs2 kvm hangs under heavy file reading

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http://serverfault.com – I have deployed four ubuntu 10.04 server. They are coupled two by two in a cluster scenario. on both sides we have software raid1 disks, drbd8 and OCFS2 and on top of it some kvm machines run with qcow2 disks. I followed this: https://wiki.ubuntu.com/ClusterStack/LucidTesting#Pacemaker.2C_drbd8_and... corosync is just used for DRBD and OCFS, the kvm machines are run "manually" When it works is fine: good performances, good I/O, but at a given time one of the two cluster started hanging. Then we tried with just one server turned on and it hangs the same. It seems to happen when an (HowTos)