On 04/08/2010 11:30 AM, Yoshiaki Tamura wrote:
If I transferred a VM after I/O operations, let's say the VM sent an TCP ACK to the client, and if a hardware failure occurred to the primary during the VM transferring *but the client received the TCP ACK*, the secondary will resume from the previous state, and it may need to receive some data from the client. However, because the client has already receiver TCP ACK, it won't resend the data to the secondary. It looks this data is going to be dropped. Am I missing some point here?
I think you should block I/O not at the cpu/device boundary (that's inefficient as many cpu I/O instructions don't necessarily cause externally visible I/O) but at the device level. Whenever the network device wants to send out a packet, halt the guest (letting any I/O instructions complete), synchronize the secondary, and then release the pending I/O. This ensures that the secondary has all of the data prior to the ack being sent out.
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