We have 2 Dell servers and a MD3000i SAN.
The configuration is the following:
\ / \ / |
X x | MD3000i
/ \ / \ |
Both hosts are Fedora 13. We use dm-multipath (multipathd). Qemu-kvm is the hypervisor.
The problem is that when host1 writes something to the SAN host 2
won’t see it until the host reestablishes a connection to the LUN (i.e. log of the iscsi targets and log in again). So writing a file on the LUN by host1 is not visible by host2 which has also mounted that LUN.
The consequense of the cachingproblem is that when a VM migrates to the other host it will crash because the virtual disk is different for host 1 and 2. Migrating with Qemu-kvm succeeds when both hosts are just rebooted.
Does anyone have a clue which component is caching? Is it the MD3000i itself? iSCSI-client (iscsiadm)? Multipathd? LVM?