White Paper The Evolution of Wide Area File Services (WAFS): Toward Transparent, Comprehensive WAN Optimization

Transcription

1 White Paper The Evolution of Wide Area File Services (WAFS): Toward Transparent, Comprehensive WAN Optimization Juniper Networks, Inc North Mathilda Avenue Sunnyvale, CA USA or 888 JUNIPER Part Number: Mar 2006

2 Introduction...3 The CIFS Mismatch...4 The Proxy Approach...5 The CIFS Challenge...6 Transparent WAFS and WAN Optimization...7 Beyond WAFS Copyright 2006, Juniper Networks, Inc.

3 Introduction Maintaining a single, centralized copy of data has always been IT s goal. Centralization ensures data consistency and simplifies everything from backups and virus checking to access control and auditing. However, the distributed nature of organizations, coupled with the slow speed and high latency of wide-area networks, has resulted in a proliferation of servers and therefore data in branch offices. Deploying file servers in branch offices gives users local area network (LAN) access to data and applications with the best performance level, but causes headaches for IT. Distributed servers are costly to manage and maintain, and lead to a proliferation of underutilized servers and storage. Application deployment is more complex, as are software upgrades and maintenance and anti-virus updates. Distributed storage poses data consistency issues for organizations in addition to backup and recovery challenges. Likewise, distributed data inhibits collaboration among employees across an enterprise, and complicates regulatory compliance. Given these drawbacks, the business trend has been to centralize applications and data. Fortunately, the emergence of wide area file services (WAFS), a technology for transferring files over wide-area links with LAN-like response times, is enabling IT to again centralize applications and data. Using a variety of acceleration techniques, WAFS products make it possible for branch office users to access centralized files as if they were stored locally. All WAFS solutions entail deploying acceleration devices at both the data center and branchoffice locations, but vendors have taken different approaches in how they accomplish file service acceleration. Some vendors offer single-function point solutions designed to accelerate file access only. These products typically operate as proxy servers. Vendors of proxy WAFS solutions tout disconnected access the ability for users to access locally cached data in the event of a WAN outage -- as a key feature of the proxy approach. However, disconnected access creates synchronization problems, posing data consistency and availability risks. In contrast, other vendors, including Juniper Networks, have designed WAFS solutions that work transparently, maintaining the direct connection of client machines in branch offices to centralized servers rather than a proxy server. In addition to providing local area network (LAN)-like performance over the WAN, this approach preserves all existing drive mappings on client machines and eliminates consistency and availability risks. Juniper is also leading the charge to deliver WAFS acceleration as an integral part of a comprehensive WAN optimization solution. File services represent a solid chunk of traffic on WAN links, but not all of it. WAFS-only solutions, therefore, accelerate only a portion of an organization s overall WAN traffic. Given an increasingly distributed workforce, the market push is for products that improve the response times of all business-critical applications. As Gartner analysts have noted, WAFS is being subsumed as one of a number of services provided by more comprehensive WAN optimization controllers. A detailed look at WAFS issues and technologies will provide a clear picture of how transparent WAN optimization products can help enterprises achieve their business objectives with data centralization -- and reap additional benefits from optimizing all WAN traffic. Copyright 2005, Juniper Networks, Inc. 3

4 The CIFS Mismatch WAFS products emerged to address the fact that, with server centralization, files that were once available to users on their local branch network now must be accessed across the WAN. Slower links, higher latency, and contention for bandwidth are only part of the performance hit that remote users experience. Further complicating remote file access is the fact that the primary protocol used for file access, the Microsoft Common Internet File System (CIFS) protocol, was designed to operate on LANs. The characteristics that make CIFS work well on LANs, however, make it painfully inefficient over WANs. Based on the Message Block protocol dating back to the mid-1980s, CIFS is the protocol Microsoft applications use to request file services from servers, supporting rich functions such as file access, file and record locking, and file change notification. CIFS runs over TCP/IP; unlike TCP, however, CIFS doesn t use a sliding window approach to ensure efficient and fair use of bandwidth. Instead, CIFS works in concert with applications to break bulk file transfers into many small data blocks from a maximum of 64 KB to as little as 256 bytes. CIFS then transmits these blocks serially. The client application and server constantly exchange messages to acknowledge and verify each block that s transmitted; the client must wait for confirmation that the last data block has been received before sending the next block. This leads to a lot of back-and-forth chatter on the network: Upwards of 1,000 CIFS messages are exchanged during the process of opening a single 1 MB Word file, for example. On a LAN, this protocol chatter has little impact on performance. WANs, however, introduce a significant amount of latency that the CIFS protocol wasn t designed to handle. Application performance degrades as the client waits for each acknowledgement; the higher the WAN latency, the worse the problem. By accelerating the CIFS protocol, WAFS products enable remote and branch-office users to access centralized data as if it were local. CIFS Clients CIFS WAN Begin Read request, Client asks for Block 1 Sends 1 st data block Client asks for Block 2 Client asks for Block 3 Sends 2 nd data block Sends 3 rd data block Client asks for Block 4 Sends 4 th data block Client asks for Block 5 Sends 5 th data block Figure 1: CIFS transmits large files serially, requiring an acknowledgement before the next block is sent. 4 Copyright 2006, Juniper Networks, Inc.

5 CIFS is used by hundreds of millions of computers running Windows and most other non windows-based computers that need to interoperate with Windows-based machines. The protocol and its implementations have evolved over the past 20 years in part from running on Xenix and OS/2 to encompass well over 100 commands. Many commands overlap for example, there are six different commands to read from a file and seven for opening a file and several commands encompass subfunctions, each with its own parameters, making for a rich yet complex protocol. CIFS implementations can vary between clients and servers, as Microsoft and other vendors put more code in client operating systems to access new features on servers and vice versa. Vendors with proxy CIFS implementations have to constantly track the entire protocol including all subfunctions and corner cases to ensure complete compliance since they emulate a server to the client and a client to the server. The Proxy Approach WAFS products implemented as proxy servers maintain cached copies of files in branch offices and synchronize with master copies of files stored in centralized servers. Since branch-office clients interact directly with the local proxy server at LAN speeds, performance is good. Proxy-based WAFS products enable enterprises to realize some business benefits of server centralization, such as eliminating underutilized file servers and storage and allowing collaboration. CIFS Clients WAFS Proxy Cached files CIFS Master files CIFS traffic XWAN Figure 2: When access to the central CIFS server is disrupted, remote users may continue working on available locally-cached copies of files on the WAFS proxy server, creating data consistency issues once the WAN connection is restored and the CIFS server attempts to reconcile different versions of the same file. However, because they are a type of server, they do little to reduce the IT burden of managing remote servers, and they also introduce data consistency and availability risks. In terms of operational overhead, IT must still deploy and maintain the proxy servers, as well as configure clients to talk to the proxy, which generally involves remapping drives. If a WAFS proxy server fails, clients cannot access the centralized server; IT must re-direct all associated clients to another proxy server, application server, or data store. In addition to requiring IT intervention, if the proxy WAFS server in a branch office fails, updates to files residing on the proxy device may be lost or discarded if users in other offices update the master copy in the meantime. That is, if users in other branch offices can access the master copy of a file, updates that a user in the downed branch made prior to the proxy failure could be discarded, placed in a file of a different name, or exiled to a quarantine area to allow a central site administrator to manually resolve update conflicts. Similar problems can arise in the event of a WAN link failure. Proxy WAFS products have a feature known as disconnected access, which allows users to continue working with locally cached data in the event the WAN link between headquarters and a branch office fails. By Copyright 2005, Juniper Networks, Inc. 5

6 definition, if a WAFS product supports disconnected access, it s functioning as a proxy server. While vendors of these solutions promote disconnected access as a benefit, it has a number of downsides. For example, if the WAN link fails, users of proxy WAFS products can operate against cached data, assuming the data they need is cached, but the level of operations that are possible varies by vendor. Some WAFS systems with disconnected access support reads only; others provide only a short window of availability after the WAN goes down. There are instances where disconnected access can pose a significant threat to data consistency and availability. If the WAFS system maintains file system locks at the server side, data consistency is maintained. However, if the user who was accessing that file is at the other end of a downed WAN link, the file will remain locked and inaccessible to other users. An administrator at the central site could break the file locks manually to make the file available to other users, but this can cause data inconsistency if the file was changed by a user at the remote site experiencing the WAN outage. Vendors and therefore customers of proxy WAFS servers face a trade off between data consistency and availability. If the WAFS device at the central site keeps open files locked in the event of a WAN outage, data integrity is maintained. However, availability suffers because any new users are locked out of the file. If the proxy WAFS server keeps the master file open, availability is maintained but data consistency is compromised since the contents of the copy maintained in the downed branch office can diverge from the master. IT also needs to consider what happens when the WAN link comes back up. If the WAFS device at either the remote or central site reboots, information about file updates and locks may be lost, making it possible for other users to access and change files. Alternately, old updates could arrive and overwrite newer updates. And what impact will synchronization traffic have on the WAN link once it s restored? Unless the WAFS product has quality of service (QoS) or other types of traffic controls, the WAN pipe may be consumed for some time with synchronization traffic, effectively extending application downtime and potentially squeezing out more important transactions. The CIFS Challenge In addition to management overhead and issues of data consistency and availability associated with disconnected access, proxy-based WAFS servers pose another challenge. Because they re a proxy for the file server, they must implement a complete version of CIFS, including bug fixes. Some vendors handle this by implementing a full-blown Windows server OS on their proxies, licensing the software from Microsoft. As we noted earlier, CIFS is an old protocol. Consequently, there are numerous variations of it, and the protocol continues to evolve. The variant of CIFS that a proxy WAFS vendor has implemented may differ from the CIFS version running on an enterprise s servers and clients. For example, there may be features such as link tracking, compression, sparse files, streams, and extended attributes that the enterprise client and server support but that the WAFS proxy doesn t. In the event of an incompatibility, the WAFS proxy downgrades file access features it doesn t support and defaults to the features it does support. Likewise, each proxy WAFS server handles access controls, auditing, and content policies differently, and may not support the policies IT already has in place. Consequently, IT needs to consider whether a proxy WAFS vendor has certified its product to work with all variations and combinations of CIFS that might be present in their organization. If not, a proxy may have problems with certain protocol semantics, policy support, or other 6 Copyright 2006, Juniper Networks, Inc.

7 CIFS features, depending on the client-server pairing. Equally important for IT to consider is that proxy WAFS products are point solutions designed to accelerate file access only. They do not accelerate the myriad of other applications that operate across the WAN, such as , web-based traffic, and other business-critical applications. Nor do proxy WAFS services address any other WAN optimization requirements, such as the need for QoS, link fail over, and other traffic management capabilities. Transparent WAFS and WAN Optimization Given the drawbacks of proxy WAFS servers and their focus on a subset of WAN traffic, several vendors, including Juniper Networks, are taking a different approach. Rather than offer enterprises a single-function WAFS product, Juniper Networks is providing WAFS acceleration as part of a complete and integrated WAN optimization solution that enables IT to improve the response time of all traffic across the WAN without having to invest in costly bandwidth upgrades or a collection of application- and protocol-specific acceleration products. WAFS is just one service available on the Juniper WAN application acceleration (WX and WXC) platforms, which provide a host of features to optimize and control WAN bandwidth, ensure data integrity and availability, and accelerate a broad range of applications and protocols. With the WX and WXC platforms, IT has complete visibility into and control over WAN traffic, allowing them to optimize application response times and maximize their WAN investments. CIFS Clients CIFS P-1 P-2 WAN Client requests Block 1 P-1 sends each block as requested P-2 requests next n blocks P-2 ACKS each block and sends to P-1 sends each block Client writes block P-1 ACKs each block and consumes server ACKs ACKs each block Figure 3: The Juniper WX/WXC application acceleration platforms transparently accelerate CIFS reads and writes without posing any threat to data consistency or integrity. Copyright 2005, Juniper Networks, Inc. 7

8 In designing its WAFS solution, Juniper Networks has taken a transparent approach to address the shortcomings of proxy WAFS servers and to meet the following requirements: To reduce the administration and management burden associated with remote servers, the WAN optimization platform should not require IT to make changes to clients (e.g., remap drives) or deploy new hardware that requires administration similar to that for a server. In the event the WAN optimization platform has an outage, no reconfiguration of it, desktops, or servers should be needed. The WAN optimization device should remain transparent to any changes in the CIFS protocol, simply forwarding messages without altering the protocol exchange between clients and servers. The WAN optimization device should not interfere with direct communications between the client and server; caching data changes locally and then forwarding them in a batch to the central site can result in data consistency issues. An optimization device must operate seamlessly within an existing WAN environment. The Juniper WX/WXC platforms are not proxy servers. Rather, employing a unique Application Flow Acceleration (AppFlow ) technology, the WX/WXC WAN optimization controllers accelerate CIFS traffic transparently, retaining direct communications between remote clients and centralized servers. The WX/WXC platforms identify and operate on individual flows between clients and servers, accelerating those aspects of file access that can be accelerated in a given flow. For example, when a CIFS client opens a file, it initiates a series of read requests. Juniper devices at the branch office and central sites work together to determine that a file is being opened and, based on the available WAN bandwidth, request the appropriate number of reads needed to efficiently fill the WAN link. By the time the client requests these data blocks, they are already stored on the client-side Juniper device and are forwarded at LAN speeds. The WX/WXC platform also accelerates directory and other file information related to a given client-server communication flow. The AppFlow technology reduces the negative effect that latency has on the CIFS protocol and accelerates data transmission significantly. For example, a 1 MB document that would take 20 seconds to copy over a 512 KB link with 100 ms of latency takes only 2 seconds with the AppFlow technology enabled. Because it s not a CIFS proxy server, the WX/WXC platforms avoid compatibility, consistency and availability problems associated with proxy WAFS server. For example, rather than attempting to emulate a CIFS server, the WX/WXC platforms support a defined set of CIFS clients and servers. Juniper avoids CIFS compatibility issues by only modifying the parts of the protocol stream where acceleration would be beneficial. Transparent TCP/IP-level acceleration and compression is always in effect, independent of what is happening at the CIFS level. At all times, clients and servers get full CIFS functionality and all access control, auditing, content, and other policies remain in force. 8 Copyright 2006, Juniper Networks, Inc.

9 Web traffic CIFS traffic WAN Web Remote Clients WAFS Proxy SAP traffic CIFS SAP Remote Clients Web WAN Compression Sequence caching QoS Monitoring Management Compression Sequence caching QoS Monitoring Management CIFS SAP Figure 4: While the WAFS proxy server optimizes only CIFS traffic, the Juniper WX/WXC platforms accelerate the delivery of all business applications, providing a comprehensive solution for optimizing WAN operations in the distributed enterprise. And because clients are always communicating directly with the server, the Juniper solution avoids the data consistency and availability issues associated with CIFS proxy servers and disconnected access. For example, should a WX/WXC platform fail, it automatically switches to bypass mode, allowing all traffic to flow across the WAN untouched, transparently ensuring uninterrupted operations. Although users may experience degraded performance due to the lack of CIFS acceleration, IT does not have to intervene to redirect clients to another server or data store, as is the case with proxy servers. In the event a WAN link fails and there is no backup or fail-over link between a branch office and centralized site, users in the disconnected office will lose access to the centralized server. However, data consistency is maintained because all files reside on the master server. Clients and servers will respond to the outage as they normally would; that is, the server will free up resources, including file locks. Because the WX/WXC platforms simply accelerate traffic and do not act as middlemen between clients and servers, both clients and servers will be fully aware of any break in their connection. Beyond WAFS As WAN optimization platforms, the Juniper WX and WXC platforms provide an array of acceleration and traffic control features beyond CIFS acceleration. Based on the integrated WX Framework architecture, the WX and WXC platforms accelerate the full range of enterprise traffic through a combination of compression, network sequence caching, QoS and TCP- and application-specific technologies. For example, the patented Molecular Sequence Reduction technology uses compression technique based on pattern matching to provide up to a ten-fold increase in WAN capacity. Similarly, the patent-pending Network Sequence Caching Copyright 2005, Juniper Networks, Inc. 9

10 technique eliminates the transmission of larger blocks of redundant traffic across the WAN and provides up to a 50-fold increase in capacity. In addition to squeezing more data onto a WAN link, Juniper provides QoS and bandwidthmanagement tools that allow IT to prioritize business-critical applications and time-sensitive traffic for more efficient link utilization. Specific Packet Flow Acceleration techniques reduce the impact of latency on TCP-based applications, while the AppFlow technology accelerates protocols for Microsoft Exchange (MAPI) and web traffic (HTTP), as well as CIFS. By design, the WX/WXC platforms do not provide disconnected access, which poses unacceptable risks. Rather, Juniper Networks believes remote offices that need continuity of operations are better served by having a secondary link, such as a DSL connection, that is automatically available in the event the primary WAN link fails. Consequently, the WX/WXC platforms offer a Policy-based Multipath technology, which allows IT to define which paths applications follow when multiple WAN links are available. The Multipath technology also supports automatic diversion to an alternate path if performance degrades below acceptable levels on one link, or if a link fails completely. Whereas the disconnected access feature of proxy WAFS devices provides limited access to cached CIFS-based data, the Multipath feature provides non-stop, accelerated access to all centralized applications and data via a backup link. Transparency is a paramount concern in a WAN optimization platform; without it, enterprises cannot reap the full business benefits of centralization. The WX and WXC platforms operate transparently to existing applications, networks, routers, and WAN interfaces as well as to IPsec VPNs, MPLS, firewalls, and encryption technologies. Ease of management is also key to lowering IT costs; in fact, it s one of centralization s main drivers. Towards that end, Juniper offers powerful management and monitoring tools such as the WX Central Management System (CMS ) software, which provides a unified view into an organization s applications and networks. In addition, the WX and WXC platforms can be installed and configured easily -- in less than 10 minutes in data centers and even more easily at remote sites, further reducing operations overhead. Integrating a range of technologies in a single platform, the Juniper WX/WXC platforms deliver WAN optimization well beyond simple CIFS acceleration. By optimizing all traffic between remote and central sites, Juniper enables enterprises to achieve the full benefits of server centralization and collaboration, simplifying the branch office architecture and reducing WAN expenses and IT operations overhead. Copyright 2006, Juniper Networks, Inc. All rights reserved. Juniper Networks and the Juniper Networks logo are registered trademarks of Juniper Networks, Inc. in the United States and other countries. All other trademarks, service marks, registered trademarks, or registered service marks in this document are the property of Juniper Networks or their respective owners. All specifications are subject to change without notice. Juniper Networks assumes no responsibility for any inaccuracies in this document or for any obligation to update information in this document. Juniper Networks reserves the right to change, modify, transfer, or otherwise revise this publication without notice. 10 Copyright 2006, Juniper Networks, Inc.