Umesh Deshpande

Gang Migration of Virtual Machines Using Cluster-wide Deduplication

Gang migration refers to the simultaneous live migration of multiple Virtual Machines (VMs) from one set of physical machines to another in response to events such as load spikes and imminent failures. Gang migration generates a large volume of network traffic and can overload the core network links and switches in a data center. In this paper, we present an approach to reduce the network overhead of gang migration using global deduplication (GMGD). GMGD identifies and eliminates the retransmission of duplicate memory pages among VMs running on multiple physical machines in the cluster. We describe the design, implementation and evaluation of a GMGD prototype using QEMU/KVM VMs. Evaluations on a 30-node Gigabit Ethernet cluster having 10GigE core links shows that GMGD can reduce the network traffic on core links by up to 65% and the total migration time of VMs by up to 42% when compared to the default migration technique in QEMU/KVM. Furthermore, GMGD has a smaller adverse performance impact on network-bound applications.

MemX: Virtualization of Cluster-Wide Memory

We present MemX -- a distributed system that virtualizes cluster-wide memory to support data-intensive and large memory workloads in virtual machines (VMs). MemX provides a number of benefits in virtualized settings: (1) VM workloads that access large datasets can perform low-latency I/O over virtualized cluster-wide memory; (2) VMs can transparently execute very large memory applications that require more memory than physical DRAM present in the host machine; (3) MemX reduces the effective memory usage of the cluster by de-duplicating pages that have identical content; (4) existing applications do not require any modifications to benefit from MemX such as the use of special APIs, libraries, recompilation, or relinking; and (5) MemX supports live migration of large-footprint VMs by eliminating the need to migrate part of their memory footprint resident on other nodes. Detailed evaluations of our MemX prototype show that large dataset applications and multiple concurrent VMs achieve significant performance improvements using MemX compared against virtualized local and iSCSI disks.

Traffic-sensitive Live Migration of Virtual Machines

Abstract 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 tra ffi c-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 pre-determined 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.

Scatter-Gather Live Migration of Virtual Machines

We introduce a new metric for live migration of virtual machines (VM) called eviction time defined as the time to evict the state of one or more VMs from the source host. Eviction time determines how quickly the source can be taken offline or its resources repurposed for other VMs. In traditional live migration, such as pre-copy and post-copy, eviction time equals the total migration time because the source is tied up until the destination receives the entire VM. We present Scatter-Gather live migration which decouples the source and destination during migration to reduce eviction time when the destination is slow. The source scatters the memory of VMs to multiple nodes, including the destination and one or more intermediaries. Concurrently, the destination gathers the VMs’ memory from the intermediaries and the source. Thus eviction from the source is no longer bottlenecked by the reception speed of the destination. We support simultaneous live eviction of multiple VMs and exploit deduplication to reduce network overhead. Our Scatter-Gather implementation in the KVM/QEMU platform reduces the eviction time by up to a factor of 6 against traditional pre-copy and post-copy while maintaining comparable total migration time when the destination is slower than the source.

Agile Live Migration of Virtual Machines

A key attraction of virtual machines (VMs) is live migration - the ability to move their execution state across physical machines even as the VMs continue to run. Unfortunately, the traditional pre-copy and post-copy techniques are not agile in the face of resource pressures at the source host, since it takes a long time to transfer the memory state of a VM. Consequently, the performance suffers for all VMs - those being migrated as well as those being left behind. Prior works have attempted to optimize indirect measures of migration effectiveness such as downtime, total migration time, and network overhead. However, none have treated the performance of VMs impacted by migration as the primary metric of migration effectiveness. We propose an Agile live migration technique that quickly recovers the performance of all VMs under resource pressure by eliminating resource pressure faster than traditional live migration. The working set of a VM is typically much smaller than its full memory footprint. Our approach works by transparently tracking the working set of each VM and offloading the non-working set (cold pages) in advance to portable per-VM swap devices. We present a new hybrid pre/post-copy technique that reduces the performance impact on the VMs workload by transferring only the working set of the VM while enabling destination to remotely access cold pages from the per-VM swap device. We describe the challenges in the design and implementation of Agile live migration in the KVM/QEMU platform without modifying the guest OS in the VM. When live migrating under memory pressure, we demonstrate a reduction in the performance impact on VMs by a up to factor of 2, reduction in migration time by up to factor of 4 besides reduction in memory pressure on both the source and destination hosts.

Performance Analysis of Encryption in Securing the Live Migration of Virtual Machines

Virtual machine (VM) migration is a technique for transferring the execution state of a VM from one physical host to another. While VM migration is critical for load balancing, consolidation, and server maintenance in virtualized data centers, it can also increase security risks. During VM migration, an attacker with sufficient privileges can compromise a VM by modifying its memory contents during transit to subvert its applications or the guest operating system. One could maintain dedicated, and presumably more secure, control networks to carry the migration traffic, but at significant hardware and administrative complexity. Alternatively, one could encrypt the migration traffic, which eliminates the need for dedicated control networks, but might introduce performance overheads. To date, there has been no systematic study of how encryption affects VM migration, especially in high-bandwidth low-delay networks that are common within data centers. In this paper, we present a study of the impact of AES and 3DES encryption algorithms on two widely used live VM migration approaches - pre-copy and post-copy. Our key findings are as follows. The encryption algorithm used can have a significant impact on the total migration time. The impact of encryption on downtime varies with the type of the migration technique. The overhead of encryption also depends upon the relative speeds of source and target machines. Finally, an applications performance within a VM during encrypted migration varies with the type of the application and the migration mechanism.

Automated and distributed protocol testing and debugging for wireless ad-hoc networks

Testing and debugging of new wireless network protocols is typically a tedious and error-prone process. Testing complex protocols requires manual configuration of numerous network testbed settings, controlled reproduction of anomalous network and protocol settings, manual traffic capture and careful analysis of protocol behavior during the test. The complexity of protocol testing grows with the length of protocol specifications and the size of the network under test. In this paper, we present the design and implementation of an automated protocol testing and analysis (APTA) tool to assist developers and protocol testers to test their protocol implementations. The central aim of our tool is to speed up the process of finding hard to reach situations where a protocol implementation may be incorrect. Our tool allows the protocol developer to specify faults using simple Netfilter/iptables-based [1] rules at run time and record the protocol responses against these faults so that the user can verify whether the protocol works as expected. Our protocol testing and analysis system allows the protocol developer to specify network events and actions in terms of distributed event-action pairs using iptables rules. For example, receiving certain number of packets of a particular protocol type can be considered as an event and delaying, modifying, or duplicating the packet or rebooting a particular node could be an action. Besides these primitive events and actions, our system also supports distributed event-action specification, which means that APTA can monitor an event on one or