We present the design, implementation, and evaluation of post-copy based live migration for virtual machines (VMs) across a Gigabit LAN. Post-copy migration defers the transfer of a VM's memory contents until after its processor state has been sent to the target host. This deferral is in contrast to the traditional pre-copy approach, which first copies the memory state over multiple iterations followed by a final transfer of the processor state. The post-copy strategy can provide a "win-win" by reducing total migration time while maintaining the liveness of the VM during migration. We compare post-copy extensively against the traditional precopy approach on the Xen Hypervisor. Using a range of VM workloads we show that post-copy improves several metrics including pages transferred, total migration time, and network overhead. We facilitate the use of post-copy with adaptive prepaging techniques to minimize the number of page faults across the network. We propose different prepaging strategies and quantitatively compare their effectiveness in reducing network-bound page faults. Finally, we eliminate the transfer of free memory pages in both pre-copy and postcopy through a dynamic self-ballooning (DSB) mechanism. DSB periodically reclaims free pages from a VM and significantly speeds up migration with negligible performance impact on VM workload.

This paper addresses the problem of simultaneously migrating a group of co-located and live virtual machines (VMs), i.e, VMs executing on the same physical machine. We refer to such a mass simultaneous migration of active VMs as live gang migration. Cluster administrators may often need to perform live gang migration for load balancing, system maintenance, or power savings. Application performance requirements may dictate that the total migration time, network traffic overhead, and service downtime, be kept minimal when migrating multiple VMs. State-of-the-art live migration techniques optimize the migration of a single VM. In this paper, we optimize the simultaneous live migration of multiple co-located VMs. We present the design, implementation, and evaluation of a de-duplication based approach to perform concurrent live migration of co-located VMs. Our approach transmits memory content that is identical across VMs only once during migration to significantly reduce both the total migration time and network traffic. Using the QEMU/KVM platform, we detail a proof-of-concept prototype implementation of two types of de-duplication strategies (at page level and sub-page level) and a differential compression approach to exploit content similarity across VMs. Evaluations over Gigabit Ethernet with various types of VM workloads demonstrate that our prototype for live gang migration can achieve significant reductions in both network traffic and total migration time.

In this paper we address the problem of network contention between the migration traffic and the Virtual Machine (VM) application traffic for the live migration of co-located Virtual Machines. When VMs are migrated with pre-copy, they run at the source host during the migration. Therefore the VM applications with predominantly outbound traffic contend with the outgoing migration traffic at the source host. Similarly, during post-copy migration, the VMs run at the destination host. Therefore the VM applications with predominantly inbound traffic contend with the incoming migration traffic at the destination host. Such contention increases the total migration time of the VMs and degrades the performance of the VM application. Here, we propose a traffic-sensitive live VM migration technique to reduce the contention of migration traffic with the VM application traffic. It uses a combination of pre-copy and post-copy techniques for the migration of the co-located VMs (those located on the same source host), instead of relying on any single predetermined technique for the migration of all the VMs. We base the selection of migration techniques on the VMs' network traffic profiles so that the direction of migration traffic complements the direction of the most VM application traffic. We have implemented a prototype of traffic-sensitive migration on the KVM/QEMU platform. In the evaluation, we compare traffic-sensitive migration against the approaches that use only pre-copy or only post-copy for VM migration. We show that our approach minimizes the network contention for migration, thus reducing the total migration time and the application degradation.

Within datacenters, often multiple virtual machines (VMs) need to be live migrated simultaneously for various reasons such as maintenance, power savings, and load balancing. Such mass simultaneous live migration of multiple VMs can trigger large data transfers across the core network links and switches, and negatively affect the cluster-wide performance of network-bound applications. In this paper, we present a distributed system for inter-rack live migration (IRLM), i.e., parallel live migration of multiple VMs across racks. The key performance objective of IRLM is to reduce the traffic load on the core network links during mass VM migration through distributed deduplication of VMs' memory images. We present an initial prototype of IRLM that migrates multiple QEMU/KVM VMs within a Gigabit Ethernet cluster with 10GigE core links. We also present preliminary evaluation on a small testbed having 6 hosts per rack and 4 VMs per host. Our evaluations show that, compared to the default live migration technique in QEMU/KVM, IRLM reduces the network traffic on core links by up to 44% and the total migration time by up to 26%. We also demonstrate that network-bound applications experience a smaller degradation during migration using IRLM.

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