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: Link
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 heavy READ in one of the virtual machines occurs, that is during rsyn backup. When the fact occurs the virtual machines are not reachable any more and the real server responds with good delay to the ping but no screen and no ssh is available.
All we can do is force shutdown (hold the button) and restart and when it turns on again the raid on which relay drbd is resyncing. All the time it hangs we see such fact.
After a couple of week of pain on one side this morning also the other cluster hung, but it has different moteherboard, ram, kvm instances. What is similar is reading for rsync scenario and Western Digital RAID Edistion disks on both side.
Can anybody give me some input to solve such issue?
UPDATE: I converted all images from qcow2 to raw and mounted the file system from within the virtual machine with noatime and nodiratime. I used ionice for rsync, but this morning it hung again while a user was reading a lot of files from a samba share. Now I am moving virtual machines imagines from ocfs2 to ext3, but it is really a defeat... any ideas are welcome.