Fault Tolerance in Virtualized Data Centers:

Transcription

1 storage without boundaries Whitepaper Fault Tolerance in Virtualized Data Centers: Leveraging the Resilience of VMware FT and StorTrends itx High Availability CERTIFIED

2 Table of Contents Introduction 3 Fault Tolerance in Virtual Machines 3 Figure 1: VMware Fault Tolerance 4 Figure 2: VMware vlockstep Technology (Active/Standby Nodes) 4 Fault Tolerance in Virtualized Storage Servers 5 Figure 3: StorTrends High Availability (Active/Active Nodes) 5 Fault Tolerance 5 Software Crashes 5 Figure 4: VMware FT and Software Crash 6 Figure 5: StorTrends HA and Software Crash 6 Software Upgrades 6 Hardware Crashes 6 Figure 6: VMware FT and Server Crash 7 Feature Comparison: VMware FT vs. StorTrends HA 7 Table 1: VMware FT Vs StorTrends HA 7 Summary 7 Trademark and Copyright Acknowledgements 9 For Additional Information 9 Limitations of Liability 9 Limited Warranty 9 Disclaimer 9 2

3 Introduction For any enterprise facing challenges in managing data effectively, one of the dominant technology trends of the day is virtualization. Virtualization also fits nicely together with consolidation, the other hot trend in today s data center. As more and more servers are virtualized, the number of disparate servers can be consolidated, as fewer physical machines are needed. Whether in the arena of application servers or storage servers, the benefits of virtualization are manifold and well understood, including: Reduced TCO Improved and centralized manageability Optimal resource utilization Less power consumption and a greener data center Reduced data center footprint Less noise Looking at the benefits in store, it is no wonder that both application and storage servers march hand in hand to the tune of virtualization. Although the future portends increased adoption of virtualization and server consolidation in data centers, like any powerful tool, proper care must be exercised in deployment, to avoid potential pitfalls. The single biggest threat that consolidated servers face is the classical all eggs in one basket syndrome. Should just one consolidated server go down, many facets of the data center will also go down along with it. To avoid this scenario, the concept of Fault Tolerance becomes very crucial. In an effort to provide an appropriate solution to this threat, VMware has introduced VMware Fault Tolerance (FT) technology into its latest product line. With a similar motivation, American Megatrends added its revolutionary High Availability technology into its StorTrends storage product line, which closely matches VMware FT in technology and often exceeds it in merits. This whitepaper will take a closer look at these two complementary fault tolerance technologies and examine the finer points of each. Fault Tolerance in Virtual Machines In any enterprise data center, the foremost concerns are data integrity and the continued availability of services. Any interruption or compromise in this area can lead to dire consequences, which are often times beyond recovery. This situation can be aggravated in data centers deploying virtual infrastructures. Because multiple virtual servers reside on a single physical server, when the lone physical server goes down, all of the virtual application servers are then put out of service. A desire to eliminate this potential problem provided the impetus behind VMware s creation of its VMware FT solution. In data centers hosting a virtual server farm, whenever FT is enabled for a virtual server, a copy of that virtual server is automatically created and run on another physical server. If the VMware Distributed Resource Scheduler (DRS) is enabled, then the most suitable system available is chosen to host this secondary VM. Alternatively, a system can be selected from a list of available servers. 3

4 Figure 1: VMware Fault Tolerance The beauty of this solution is that it is OS independent, meaning that any application server may be enabled with VMware FT irrespective of the OS or application it is running. There is no need to make any changes to the OS or application to support this fault tolerance. There are, however, some specific requirements with respect to the hardware components (such as the CPU) in order for VMware FT to be deployed successfully. Also, there is a rigid requirement for the two VMs (Primary and Secondary) to be running identical OS and application codes. VMware utilizes an innovative vlockstep technology to ensure this fault tolerance, which assures that the two VMs run exactly identical code in synchronization. The primary VM delivers all non-deterministic events and packets like keyboard, mouse and network inputs to the secondary VM over a high-speed network link. The following diagram illustrates the data stream that is shipped to the secondary VM from the primary via vlockstep. Figure 2: VMware vlockstep Technology (Active/Standby Nodes) In cases where the primary VM becomes unavailable due to the failure of the primary server, the secondary VM immediately assumes the role of the primary. To ensure transparent failover, VMmware utilizes a network virtualization mechanism, where the complete network identity of the primary VM is taken over by the secondary VM. Note that the VMware infrastructure may also automatically elect another physical server to host a new secondary VM to ensure future fault tolerance. 4

5 Fault Tolerance in Virtualized Storage Servers A data center deploying a virtualized server infrastructure requires one or more shared virtual storage servers to host the data stores for the VMS. It is absolutely necessary for the shared storage server to also be adequately robust and fault-tolerant. The HA component of StorTrends itx is quite capable of supporting such stringent demands. This architecture is designed to be used in virtualized environments in the same manner as it would be deployed for application servers, where a separate StorTrends server is used to act as the secondary storage. During configuration, all that needs to be done is simply to select an appropriate secondary server and enable HA StorTrends itx takes care of the rest. Unlike VMware FT, which relies on underlying shared storage, StorTrends HA employs mirrored storage; this way, there is no common or shared resource between the two nodes, allowing the two servers to offer complete site fault tolerance. Figure 3: StorTrends High Availability (Active/Active Nodes) The HA architecture in StorTrends itx uses Resource Groups to provide an extremely efficient load balancing capability. The volumes residing in the StorTrends servers can be divided into two Resource Groups (RG). From here, one StorTrends server may serve as the primary server for one RG and the second StorTrends unit may assume the primary role for the other RG. The owner of the RG is responsible for mirroring all data writes to its peer. The benefits of this requirement are twofold: first, the compute and I/ O loads are shared by the two servers, and as such, each plays an active role for an RG. Secondly, since the disk writes are mirrored to the peers in two different directions over the network link (one from A to B and the other from B to A), the link bandwidth is used much more efficiently over the full-duplex links. In the event of a server failure, the surviving StorTrends server takes on the primary role for both Resource Groups. Because StorTrends employs Network Virtualization, the surviving server takes over the entire network identity of the failed server, so the failover unfolds transparently and in an OS-agnostic manner. Fault Tolerance In today s highly demanding data center environment, a wide range of threats to the enterprise could adversely affect its operation and availability in an instant. The following sections will take a brief look at some of these potential hazards and effects on a datacenter deploying VMware FT and StorTrends HA. Software Crashes The threat of a software crash is omnipresent and all too familiar these days, whether on physical or virtual servers. The OS of a virtual machine can crash due to bugs in the kernel, creating a temporary loss of the server. Applications running in the virtual machine service can also crash or terminate abnormally, resulting in service unavailability, and virus intrusions can also lead to service interruptions, at a minimum - or possibly much worse. 5

6 Figure 4: VMware FT and Software Crash Such events, unfortunately, are not well negotiated by VMware FT. The reason for this is obvious, as both the primary and secondary VMs execute identical software code and are thus prone to identical consequences. Therefore, a crash in the primary VM will also result in a crash in the secondary VM, leading to a disruption in service availability. In contrast, High Availability in StorTrends itx enables the secondary StorTrends node to continue to run, even in cases where the primary server goes out of service due to a software crash. This survivability of the second node ensured is because the two nodes do not execute identical code in lockstep. In situations where the primary goes down, the secondary node will take over the role of the primary, and the storage cluster will continue to offer service with no compromise in its availability. Software Upgrades Figure 5: StorTrends HA and Software Crash Periodically, every server needs to be updated with software upgrades, whether for security fixes, bug fixes or a number of other reasons. Since VMware FT requires identical software code to be running in both VMs, in order to upgrade or update software, one has to bring down both the VMs, upgrade the software and then bring them back up. Of course, during this time, the VM cluster will be unavailable. With StorTrends, unless the update is for a major version upgrade, each node can be updated independently, while the other node continues to serve the storage cluster, keeping it available throughout the update process. Hardware Crashes With VMware FT, in the event that the primary VM node goes out of commission as a result of hardware or power failures, the secondary VM node will always be available to take on the primary role. As such, hardware failures will not impact service availability in any way. 6

7 Figure 6: VMware FT and Server Crash With StorTrends HA, the scenario remains the same. If the primary node becomes unavailable due to hardware or power failure, the secondary node will assume the role of the primary and the storage cluster will remain available. Feature Comparison: VMware FT vs. StorTrends HA Summary Feature VMware FT StorTrends HA Technology VLockStep (Log Replication), Network Virtualization, Server Virtualization OS-independent Yes Yes Bidirectional I/O Replication, Network Virtualization, Storage Virtualization Storage Architecture Shared Storage Mirrored Storage Peer Replication Reads / Writes / Non-deterministic Events Writes Software Upgrade Requires scheduled downtime Cluster remains available Hardware Crash System remains up; auto failover System remains up; auto failover Software Crash Cluster goes down Cluster remains available Peer Functionality Active / Standby Active / Active Table 1: VMware FT Vs StorTrends HA With virtualization assured of making continuous inroads into the data center, the issue of fault tolerance continues to grow in importance. Many players are jostling for space and attention in the server virtualization arena, but VMware has emerged as the leader of the pack by virtue of its feature-rich offering. Its latest addition of the VMware FT service once again fits into a sweet spot by addressing the issues of robustness and reliability of virtual server farms. VMware FT enables enterprises to implement server virtualization in an OS neutral and platform agnostic manner. It is undoubtedly a powerful feature, yet one that it is still in its infancy and limited to a certain extent. At present, only single processor VMs are supported, due to the technical complexities of handling multiple CPUs in such an environment. VMware also recommends that as a best practice, other subcomponent level redundancies, such as network teaming, should be implemented - even when FT is deployed. A key component of a virtualized datacenter is the shared storage server. The availability and fault tolerance of this underlying storage server is also critical, and the High Availability capabilities of StorTrends itx makes it a very attractive candidate for virtualized storage servers in these scenarios. Regardless, like VMware FT, it is recommended to implement sub-component level redundancies, including RAID for disk failures and network teaming for network-related irregularities. 7

8 When VMware FT and StorTrends HA are deployed together in a datacenter, in addition to the many powerful features that these two products provide, the comfort of heightened robustness and fault tolerance is an added benefit. Hopefully, after reading this whitepaper you have gained a better understanding of these two fault tolerance technologies and some of their similarities and distinguishing features. For more information on the HA component of StorTrends itx, as well as details on the complete line of StorTrends IP-SAN and NAS storage appliances, please contact a StorTrends Sales Associate at U-BUY-AMI, or visit AMI on the web at www. StorTrends.com. 8

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10 Whitepaper This publication contains proprietary information that is protected by copyright. No part of this publication can be reproduced, transcribed, stored in a retrieval system, translated into any language or computer language, or transmitted in any form whatsoever without the prior written consent of the publisher, American Megatrends, Inc. American Megatrends, Inc. All Rights Reserved American Megatrends Inc Oakbrook Parkway, Suite 200 Norcross GA t: Sales & Product Information sales@ami.com t: Technical Support support@ami.com t: