Tech Sheet Benefits of Dual Redundant Active/Active Storage Architecture

Transcription

1 Tech Sheet Benefits of Dual Redundant Active/Active Storage Architecture Tech Sheet

2 Introduction Storage servers constitute the very foundation of any data center and their features, performance and scalability remain the yardsticks for by which their effectiveness is chiefly measured. However, while these aspects are undoubtedly important, they assume a secondary role behind three core attributes that gauge storage server effectiveness: reliability, availability and serviceability (or maintainability). A Storage server may offer outstanding I/O performance or a wealth of features, but if it does not guarantee excellent reliability and availability then it stands on a very weak foundation. As technology trends like virtualization and consolidation approach the point of near-ubiquity, servers are subjected to diverse and very intense I/O loads. Therefore, in addition to offering strong performance it is equally essential that the storage server should guarantee highly available and highly reliable data services with excellent serviceability. In simplest terms, reliability can be defined as the probability that the system s hardware and software components will offer fault free services over a specified period of time. Data corruption, component failures and software crashes are the primary factors that impact storage server reliability. As such, Mean Time between Failures (MTBF) is a good yardstick for gauging reliability. Availability is a measure of system up-time and is expressed as a percentage of (UP TIME) / (UPTIME + DOWNTIME). For enterprise-grade servers the requirement of availability is generally Five Nines, or % availability which translates to about five minutes of downtime in a year. However, while reliability, availability and serviceability are key parameters of storage server effectiveness, some interdependence exists between them; for example, high availability demands high reliability and high serviceability (low service time). High Availability with Active/Active Architecture The underlying principle behind High Availability (HA) is component redundancy. RAID protection and redundant Field Replaceable Units (FRU) are commonplace but controller redundancy, seen only in high-end storage servers, is essential to guarantee Five Nines availability. In basic terms, there are two ways in which controller redundancy may be implemented. The first is to duplicate the entire hardware configuration, including the disks, and keep the two storage servers in sync using synchronous replication or mirroring. The other, more economical alternative is to employ dual controllers housed in a single chassis, using shared storage protected by RAID. Irrespective of the strategy employed, the redundant units may work either in Active/Standby (A/S) or Active/Active (A/A) mode. In the former, one controller or server is active and the other plays a wait and watch role. In the event of the active unit s Tech Sheet 2

3 failure, the standby unit takes control. Active/Active architecture, on the contrary, has both of the controllers actively engaged in serving data. In the event of a controller failure, the surviving unit takes on the added load to assure service availability. Experience shows that Active/Active configurations are the preferred configuration of the two, as they offer higher performance and better resource utilization. In an Active/ Standby configuration only one set of network links are actively engaged in offering I/O services, while in an A/A architecture the network bandwidth is effectively doubled. More importantly, each of the multi-core CPUs in both controllers is actively engaged in serving I/Os, to double the compute power of the storage server. Another benefit of an A/A configuration - perhaps less tangible but equally important - is the effective doubling of memory bandwidth and memory capacity. As bandwidth doubling improves throughput, the doubling of memory capacity improves cache performance by increasing the cache-hit ratio. Because proper implementation of an Active /Active server configuration can be challenging, most traditional storage vendors settle with Active/Standby offerings, in spite of the many advantages that A/A provides. In contrast, StorTrends incorporates Active/Active architecture in both mirrored-storage and shared-storage configurations. NIC NIC CPU CPU Memory Midplane Memory Active/Active Storage Server Architecture Disks Disks Active/Active Storage Server Architecture StorTrends leverages state-of-the-art I/O and resource partitioning strategies to effectively implement Active/Active configurations. Naturally, the biggest challenge in an A/A environment is keeping the two sides working coherently while server states and metadata changes undergo constant synchronization. To achieve this, StorTrends utilizes a very fast and effective synchronization architecture based on an efficient and patented log shipping mechanism. StorTrends also provides excellent I/O performance by enabling the peer controllers to work in write-back modes in contrast to most other storage vendors, who settle for write-through mode to avoid implementation related difficulties. To further enhance performance and reduce latency, StorTrends employs two redundant high-speed (10 Gig) links in a load-balanced configuration employing super-jumbo frames. Tech Sheet 3

4 Another common cause of service unavailability is software updates and upgrades. Most software undergoes frequent enhancements by way of feature additions and security or bug fixes. This presents a special problem for dual controller servers, like those commonly offered by many storage vendors, since standard practice is to upgrade and reboot both controllers simultaneously. In these cases, service remains unavailable for a short interval and is viewed as a scheduled maintenance disruption. However, StorTrends itx network storage software anticipates this potential problem and is carefully designed to not cause any disruptions during such updates - even in an Active-Active dual controller setting. With StorTrends, upgrades are automatically applied in a sequential manner to ensure that at least one controller is always available. Why StorTrends for High Availability? StorTrends advantages include: Dual-active controllers offer excellent availability Active-Active implementation doubles bandwidth and compute power, enhances cache performance Active-Active configuration for both mirrored storage and shared storage Availability is retained even during software malfunctions and crashes Software updates are transparent, without causing maintenance related disruptions Fast log-shipping for synchronization and coherency of Active/Active controllers Active-Active setup with write back cache offers high I/O performance and low latency Proactive pre-failure analysis and maintenance ensures high serviceability and availability Additionally, to guard against generic system software failures StorTrends offers built-in safety features to detect malfunctions and prompt the affected unit to either perform a selfreboot or permit the peer to reboot it via IPMI controls. During the short interim period until the faulty controller resumes normal service, the peer unit takes over to avoid disruption of availability. And because server availability goes up if system serviceability is improved, StorTrends employs extensive system monitoring and a number of proactive, online prefailure maintenance strategies to ensure high serviceability and availability. Why StorTrends? StorTrends from American Megatrends, Inc. is Performance Storage with Proven Value. StorTrends SAN and NAS storage appliances are installed worldwide and trusted by companies and institutions in a wide range of industries including education, energy, finance, state & local government, healthcare, manufacturing, marketing, retail, R&D and many more. StorTrends enables users with the features and tools necessary to meet the challenges and demands of today s business environments by offering key network storage functionality such as unified storage, simplified management, business continuity, disaster recovery, high efficiency and virtualization support. Since 2001, StorTrends has built a Tech Sheet 4

5 community of over 1,000 satisfied customers thanks to award-winning products, integrated data protection and world-class support, while continuing to enhance its products with patented enterprise-class features. For more information on StorTrends solutions from AMI, visit to or call U-BUY-AMI. Tech Sheet 5