WHITE PAPER Riverbed SteelFusion Extending storage across the WAN for complete edge consolidation
Introduction While some organizations are small or simple enough that they require only a single location, many businesses have a large number of offices or branches sometimes hundreds or even thousands of distinct sites. Though business objectives require people to be present in these locations, it does not automatically follow that all of those sites require the same IT infrastructure. Best practices have dictated the deployment of servers and storage close to users to offer fast access to applications and data. This approach however adds significant burden to the IT organization that must manage server and storage provisioning, system management, data protection, and recovery for numerous remote locations. In recent years, IT organizations have undertaken consolidation initiatives through shared storage and virtualization to build centralized, flexible infrastructures. Despite these efforts, a significant amount of IT equipment largely still remains in edge locations which increases cost and burden, and distracts from more critical goals of an organization. Organizations are ripe for a solution to the challenge of distributed infrastructure to lower costs, ease management burdens, guarantee business uptime, and ensure security of valuable data. The limitations of legacy solutions When servers and storage are deployed in branches, the result is an archipelago a sprawling collection of small islands of servers and storage. There are many distinct items to be managed, and each is separated in a way that makes it very difficult to effectively share resources. This infrastructure at remote sites is needed for higher performance but fall into a no-man s land between branch and IT it s critical for branch performance, but requires IT management skills that may not be present in a branch. Additionally, it has to be managed by IT but is typically a duty that is not primary to larger IT goals in the data center. Rather than managing remote servers, storage, and data, many organizations embarked on consolidation projects to centralize the common services required by users across the organization. One of the key challenges of moving applications and data distant from users is performance. Bandwidth and latency constraints impact the speed at which users can access and utilize centralized resources. Wide area network (WAN) optimization solutions help resolve performance problems, but is still surprisingly common for enterprises to maintain IT infrastructure at branch offices. File and application servers, disks such as direct attached storage (DAS) or small network attached storage (NAS) arrays and a backup solution often remain in the branch due to two primary reasons: Performance The performance requirement of the application or workload is higher than can be delivered across the WAN even with optimization Offline operations Organizations want to ensure that remote business offices in locations where network infrastructure is unreliable can remain productive during network failures Characteristics of applications that remain decentralized Applications that continue to be hosted in branch locations instead of the data center include local authentication and print services, high-speed file serving, and database or custom applications that are needed by users at the edge: Content creation at the edge: Applications that create new content in the remote office common in organizations such as advertising agencies, law firms, banks, and military/intelligence agencies typically required local infrastructure to deliver adequate write-performance. When a workload demonstrates random I/O or performs a high number of smaller sized read/write operations, having the ability to save and store locally is critical. Challenging I/O requirements: Applications such as databases or virtual desktop infrastructure generate random I/O or are very sensitive to latency. These applications therefore require compute to be present at the edge along with fast local storage. 2014 Riverbed Technology. All rights reserved. 1
Custom applications: Many organizations develop applications that cater to the specific needs of their industry and office. These homegrown applications are maintained in the branch location where they are used by the local user population. Limitations to consolidating storage and servers In an ideal scenario, all IT assets would be provisioned, managed, and protected in the data center. As outlined above, centralization and consolidation to the data center often compromises branch user performance. How then might it be possible to enable centralization and consolidation for these difficult cases? Since storage is a common denominator for all of the servers and applications required at the edge, could just the storage component be centralized to enable IT to regain control of orphaned islands of data? Block-access latency Applications are commonly written with the assumption that speed of storage access will be optimal either via direct attached storage (DAS), network attached storage (NAS), or a storage area network (SAN). Database applications for instance even non-critical ones expect the block-access layer latency to be on the order of microseconds. When provisioned in the data center, storage connected via low latency IP or Fibre Channel networks delivers extremely fast access to local applications and hosts. Solutions such as 8 Gb/sec Fibre Channel fabric and 10Gb/sec IP networks eliminate latency as a factor for network-based block-device access. While it is possible to see storage over a WAN, in practice, block-access latency has prevented servers and applications from effectively using remote storage. When applications experience latency in the block layer, the resulting response is typically a stall with serious errors or, in some cases, the inability to recover gracefully. The inability of applications to cope with block-access latency prevents storage from spanning extending to a branch office across a WAN and, therefore, dictates that storage and compute be coupled together in the same physical location. Block-access patterns I/O activity at the SCSI or Fiber Channel layer does not follow a sequential block access pattern. Sequential file system block addresses do not usually translate to sequential physical block addresses on the storage device. While a file system such as NTFS or VMFS formatted on top of a block device has a virtually contiguous view of stored data blocks, the actual physical block layout on the device such as the back-end SAN array, does not follow a contiguous pattern. The random nature of physical device block allocation has defied traditional acceleration techniques because data access patterns are random and not predictable. Riverbed SteelFusion decouple storage from compute for complete data centralization Riverbed SteelFusion branch converged infrastructure solves the problem of delivering local branch performance from data center storage over the WAN, enabling organizations to centralize data in the data center while ensuring applications at the edge perform at LAN speed. SteelFusion appliances decouple storage from compute enabling physically centralized but logically distributed data at the block level. Compute resides independently at the branch for high-speed local performance, while SteelFusion accelerates block access across the WAN from a common pool of storage on the data center SAN. This new architectural approach is called edge virtual server infrastructure (edge- VSI) and delivers two key capabilities: Central administration of storage serving a large number of locations, diverse file systems, and diverse applications Common data protection applied across locations, file systems, and applications centrally in the data center These powerful capabilities allow organizations that deploy SteelFusion appliances to: Streamline and consolidate branch infrastructure 2014 Riverbed Technology. All rights reserved. 2
Eliminate the need for remote backups or replication over the WAN Extend storage best practices likes snapshots, and archiving and backup policies to branch data Instantly provision servers in support of enterprise wide virtualization initiatives Provision, patch and maintain edge servers centrally Simplify disaster recovery How it works To deal with the random I/O and latency of reads, SteelFusion brings file system awareness to the block layer. File system awareness enables intelligent block prefetch that addresses both high latency and the inherently random nature of I/O at the block layer, accelerating block storage access across distance. To eliminate latency introduced by the WAN, the SteelFusion appliance in the branch presents itself as a write-back block cache. Block writes by applications and hosts at the edge are acknowledged locally and then asynchronously flushed back to the data center. By combining these read/write optimization techniques, SteelFusion is able present a virtual storage LUN to applications and hosts at the branch across a WAN, while the underlying physical storage LUN is provisioned at the data center. To an application server and file system running at the edge, data center storage mapped on the SteelFusion appliance in the branch appears just like a local block-storage device. SteelFusion allows data center architects to achieve the consolidation nirvana that was not possible before. Tight coupling between compute and storage made storage asset consolidation and the need for high performance at the branch two conflicting goals. SteelFusion untangles these goals by enabling data center architects to position compute close to the user at the network edge for an ideal user experience while simultaneously managing all storage and protecting all data centrally at the data center. SteelFusion components SteelFusion, as shown below in Figure 1, has two logical components: SteelFusion Core and SteelFusion Edge. SteelFusion Core is a physical or virtual appliance in the data center, and it mounts all the LUNs that are to be made available to applications and servers at a remote location from the back-end storage array. SteelFusion Core makes those LUNs available across the WAN in the branch via the SteelFusion Edge module on a Steelhead EX or standalone SteelFusion appliance. SteelFusion Edge in the branch presents the LUNs projected from the data center as local iscsi LUNs to applications and servers on the local branch network and operates as a block cache to help ensure local performance. For writes SteelFusion Edge acknowledges all writes locally to ensure high-speed ( local ) write performance. SteelFusion maintains a write block journal and preserves block-write order to keep data consistent in case of a power failure or WAN outages. For reads The SteelFusion Edge cache is warmed with relevant data delivered by SteelFusion Core in the data center, which performs predictive prefetch to ensure required data is quickly delivered. Alternatively, a LUN can be pinned all data from the data center LUN can be prepopulated to the edge cache SteelFusion appliances also take advantage of Steelhead WAN optimization at both the data center and edge for network deduplication and TCP-based acceleration to make sure that data is optimally transported between branch and data center. 2014 Riverbed Technology. All rights reserved. 3
Figure 1 SteelFusion appliances enable branch servers to leverage data center storage Write-back block cache SteelFusion Edge acknowledges all iscsi write operations locally. It caches the incoming writes locally on disk and then asynchronously flushes them back to the data center storage array via the SteelFusion Core. This enables application and file system initiator hosts in the branch to make forward progress without being impacted by WAN latency. As blocks are received, written to disk and acknowledged, the written blocks are also journaled in write order to a log. This log file is used to maintain the block-write order to ensure data consistency in case of a crash or WAN outage. When the connection is restored, SteelFusion Edge plays the blocks in logged write-order to SteelFusion Core, which commits the blocks to the physical LUN on the back-end storage array. The combination of block journaling and write-order preservation enables SteelFusion Edge to continue serving write functions in the branch during a WAN disconnection. File system and application awareness To overcome block access latency on data reads SteelFusion Core performs block-level prefetch from the back end storage array and actively pushes blocks to SteelFusion Edge to keep its cache warm with a working set of data. To accomplish this prefetch, SteelFusion first establishes file system context at the block layer. For Windows servers (physical or virtual) for instance, SteelFusion Core crawls the NTFS Master File Table (MFT) to build a two-way map of the file system blocks to files, and files to blocks. This map is used to determine what to prefetch. By intelligently inspecting iscsi block access requests from the application/host file system iscsi initiator, SteelFusion algorithms predict the next logical file system block or a cluster of blocks to prefetch. Disconnected operations In some cases, the WAN connection may suffer an outage or may be unpredictable. That means that branch-resident applications might behave unpredictably in case of a block cache miss and cannot be serviced from the data center SAN due to the WAN outage. For such cases, SteelFusion implements a feature called LUN-pinning. With LUNpinning, the contents of an entire LUN are prefetched from the data center and prepositioned at the edge to ensure a 100% hit rate on SteelFusion Edge. In LUN-pinning mode, no reads are sent across the wire to the data center, although dirty blocks (changed/newly-written blocks) are preserved in a persistent log and flushed to the data center when WAN connectivity is restored, ensuring consolidation and protection of newly created data. The result is high performance for applications during a WAN outage, whilst extending continuous data protection to the edge. 2014 Riverbed Technology. All rights reserved. 4
Boot over the WAN VMware vsphere virtual server technology combined with SteelFusion now makes it possible to boot over the WAN to provide instant provisioning and fast recovery capabilities for edge locations. As shown in Figure 2, a bootable LUN in the data center is mapped to a host in a branch office. The host can either be a separate ESXi server or the Steelhead EX appliance Virtual Services Platform (VSP). SteelFusion Core detects the LUN as a VMFS file system with an embedded NTFS file system virtual machine workload and upon further inspection learns the block sequence of both. Once the boot process in the branch starts, iscsi blocks for the Windows file server virtual machine are requested from across the WAN. SteelFusion Core recognizes these requests and prefetches all of the required block clusters from the data center provisioned LUN and aggressively pushes them to the SteelFusion Edge appliance at the branch. Prefetching results in a 100% block hit rate on the SteelFusion Edge appliance in the branch, ensuring local performance for the boot operation. This same file system aware prefetch also predicts operations like file access and large directory browsing thereby providing seamless access to LUNs which are across a WAN. A Windows server is a common branch component. SteelFusion appliances enable local performance while delivering server and storage consolidation in scenarios where true LAN performance is required to service workloads like random or small file I/O. The virtualized server instance is now delivered virtually across the WAN along with user and application data. Figure 2 - SteelFusion enables fast boot over the WAN 2014 Riverbed Technology. All rights reserved. 5
Sample performance results Riverbed has performed several SteelFusion tests, including a VMware-based virtual instance of a Windows Server boot. To solely focus on the effectiveness of the SteelFusion prefetch techniques and write-back cache, the test scenario pre-warms the Steelhead appliance data store to ensure it is excluded from the performance measurement. The table below shows the duration of the boot process for a typical virtualized Windows Server from a bootable-lun mapped across a 1.5mbit/sec DSL connection with 100 milliseconds of round trip latency in a deployment similar to the configuration illustrated in Figure 2. Steelhead Data Store SteelFusion Cache Time (minutes) WARM COLD 4 WARM WARM 2.5 No Steelhead No SteelFusion Times-out/Does not work The four minute Windows Server boot time across a high latency WAN with a cold SteelFusion Edge is dramatically better than the base case without the Steelhead and SteelFusion solution combination in which the boot process times-out after an hour. This illustrates the effectiveness of file system-aware block prefetch designed to ensure that a fully functional virtual server can boot and function over distance as if its storage is present locally. Once the desktop boots, all typical tasks like browsing directories, exporting file shares, and document editing function normally as if storage is attached locally even though it is being managed centrally on enterprise storage. Once the SteelFusion Edge cache is warm, the boot times are similar to how a locally mapped LAN-based bootable LUN would perform. Conclusion The benefits of a well-planned and executed consolidation approach can extend beyond merely cost savings, with companies improving the way they mitigate risk and grow. By enabling LAN performance at the edge via centrally managed storage, SteelFusion makes the stateless branch possible. Servers are available to deliver on user requirements in the branch, yet centrally provisioned, managed and protected. The SteelFusion module is an extension of the Riverbed Steelhead WAN optimization platform for the distributed enterprise and delivers new consolidation possibilities for applications, servers, and systems that are distributed geographically throughout an organization. Organizations now have a way to extend the boundaries of the data center to deliver real-time services from centrally managed infrastructure. By extending centralized storage, server, application, and data protection best practices to serve the needs of remote locations, Riverbed helps IT organizations reduce complexity while continuing to meet enduser performance requirements. all at a lower cost of ownership. About Riverbed Riverbed at more than $1 billion in annual revenue is the leader in Application Performance Infrastructure, delivering the most complete platform for Location-Independent Computing. Location-Independent Computing turns location and distance into a competitive advantage by allowing IT to have the flexibility to host applications and data in the most optimal locations while ensuring applications perform as expected, data is always available when needed, and performance issues are detected and fixed before end users notice. Riverbed s 25,000+ customers include 97% of the Fortune 100 and 95% of the Forbes Global 100. Learn more at www.riverbed.com. Riverbed Technology, Inc. 680 Folsom St. San Francisco, CA 94107 Tel: (415) 247-8800 www.riverbed.com Riverbed Technology Ltd. One Thames Valley Wokingham Road, Level 2 Bracknell. RG42 1NG United Kingdom Tel: +44 1344 31 7100 Riverbed Technology Pte. Ltd. 391A Orchard Road #22-06/10 Ngee Ann City Tower A Singapore 238873 Tel: +65 6508-7400 Riverbed Technology K.K. Shiba-Koen Plaza Building 9F 3-6-9, Shiba, Minato-ku Tokyo, Japan 105-0014 Tel: +81 3 5419 1990 2014 Riverbed Technology. All rights reserved. 6