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Cisco Wide Area Application Services (WAAS) Appliances

Cisco Wide Area Application Services Optimizations for File Server Protocols

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Cisco® Wide Area Application Services (WAAS) Version 4.0 provides significant throughput improvements for remote-office users accessing centralized file servers or network-attached-storage (NAS) devices using the Common Internet File System (CIFS) protocol. This document discusses the optimizations that Cisco Systems® provides through Cisco WAAS that apply specifically to file services

CHALLENGE

Enterprise IT organizations are being challenged to centralize distributed file server infrastructure to maintain compliance, improve data protection and retention, and control costs. Network file access protocols such as CIFS provide network users with safe access to a file system on a server, but must also maintain the semantics of the file system of the local file server. To maintain these semantics, a large number of message exchanges must occur before the first segment of information can be served to a requesting user. When such "chatty" protocols are used in an environment with high latency, packet loss, and bandwidth constraints such as a WAN, file server access over the WAN is significantly diminished. To meet these challenges, IT organizations have been deploying local file services infrastructure at locations where more than just a few employees reside, as shown in Figure 1. For each silo of file services deployed, data protection equipment and other costly components must be installed as well.

Figure 1. Typical Distributed Enterprise Infrastructure

With Cisco WAAS and the Cisco Wide Area Application Engine (WAE) Appliances and router-integrated network module, enterprise IT organizations can now safely centralize distributed file server and NAS infrastructure in the data center without compromising the performance of the remote-office user, as shown in Figure 2.

Figure 2. Centralized Infrastructure with Cisco WAAS

FILE SERVICES APPLICATION ACCELERATION

Cisco WAAS provides robust application acceleration for the CIFS file access protocol. With these optimizations, remote-office users enjoy LAN-like access to centralized file server or NAS storage capacity. Cisco WAAS file services optimizations include the following:

• Latency mitigation-The file services application adapter examines protocol messages to determine which messages can be safely handled locally, which messages can be safely suppressed, and which messages must traverse the WAN to maintain protocol correctness, data integrity, and user authenticity. Furthermore, Cisco WAAS can apply optimizations to operations to improve efficiency, including read-ahead caching, message prediction, and operation batching. Through intelligent protocol message handling, Cisco WAAS effectively eliminates up to 99 percent of the perceived WAN latency.

• Bandwidth consumption control-The file services application adapter has a file data cache that serves usable files directly to the user. After validation that the file has not changed, Cisco WAAS locally serves information to the requesting user. By serving information locally, Cisco WAAS avoids wasting WAN bandwidth. Furthermore, files can be prepositioned at remote-office Cisco WAE appliances or network modules to improve performance for first-user access.

• Integration with WAN optimization-Cisco WAAS provides industry-leading WAN optimization capabilities, including advanced compression and TCP optimizations. The file services application adapter uses these WAN optimization capabilities to help ensure that any message or transfer of file data traverses the WAN in a highly efficient manner. WAN optimization is particularly effective in operations such as changing file names, opening files, and saving files. Because Cisco WAAS advanced compression is protocol- and file-independent, it can make use of the data commonalities found in other files and data transmitted using other protocols, as shown in Figure 3.

Figure 3. Cisco WAAS File Services Acceleration and WAN Optimization

• Disconnected mode of operation-The Cisco WAAS file services application adapter allows IT organizations to specify which file servers should be available in read-only mode when the file server is unreachable. With this setup, users who are successfully authenticated on a domain controller can continue to access files that are fully cached even during periods of WAN disruption. The disconnected mode of operation helps minimize the disruption to user productivity when network outages or server outages occur.

• Local print services-Many remote-office file servers act as print servers, and removing the file server forces user print traffic to traverse the WAN. With Cisco WAAS, a local print server can be configured so that print traffic does not need to traverse the WAN. Furthermore, the Cisco WAAS Central Manager manages the distribution of drivers and monitors service availability.

Employing application-specific acceleration and WAN optimization capabilities gives users in remote-offices who access centralized file servers LAN-like access to the files they need, as shown in Figure 4.

Figure 4. Cisco WAAS LAN-Like Access to Centralized File Servers and NAS Devices (T1 Line with 80-ms Round-Trip Time [RTT])

CISCO WAAS MAINTAINS DATA INTEGRITY AND SECURITY

The Cisco WAAS file services application adapter is designed to maintain file access protocol correctness and integrates transparently into existing networking environments. By allowing integrity-critical messages to propagate synchronously to the file server, Cisco WAAS helps ensure that data is not corrupted, outdated (stale) data is not served, and security semantics are not compromised.
Cisco WAAS file services are designed to do the following:

• Never serve outdated data-If a file that is stored in the file cache of the Cisco WAE is requested, a validity check is performed against the origin file server to make sure that the cached version is identical to the version on the file server itself. If the versions are identical, the file is served to the requesting user. If the versions are different, the file is completely removed from the file cache and is requested from the origin server. If a requested file is not stored in the cache, Cisco WAAS WAN optimization capabilities such as advanced compression and TCP optimizations are applied to minimize the amount of data that must actually traverse the network. Under no circumstances does Cisco WAAS serve stale data to a requesting user.

• Facilitate global collaboration-Cisco WAAS file services does not proxy lock requests near the user. Instead, Cisco WAAS passes lock requests to the origin file server for native handling. Allowing the origin file server to handle lock requests allows users from many sites (with or without Cisco WAAS) to safely share data and collaborate globally.

• Integrate with existing file server security-Cisco WAAS transparently passes user session information to the origin file server to provide smooth integration with existing file server security and permissions configuration. The file server actually sees the user who is attempting to access the file server and handles permissions and security in the normal way. Security and permissions are fully preserved, as are additional file server features such as disk quota enforcement and auditing.

• Adapt to changes in connectivity-The file services adapter is designed to safely handle failure conditions that may arise in the network, client, server, or Cisco WAE. For intermittent outages, the Cisco WAE can mask disconnections for up to 90 seconds. During this period, the Cisco WAE attempts reconnection while maintaining the session state (including file handles and file locks). If the Cisco WAE can successfully reconnect, the network outage is safely masked from the user and the server. After 90 seconds, the Cisco WAE transitions to disconnected mode, in which the session state is cleaned up on the file server and with the client. Thus, no stale state (such as file locks) remains after disconnection. For servers configured with disconnected mode, users who can successfully reauthenticate can access cached content in read-only mode.

INTELLIGENT FILE PREPOSITION

With its understanding of and interaction with client and server communications, Cisco WAAS is well-positioned to provide value-added services for file access. One example of such a service is intelligent file prepositioning. Prepositioning is the scheduled acquisition and distribution of file data to prepopulate Cisco WAE caches with file information. Prepositioning a file in the Cisco WAE cache dramatically accelerates the first user access to the file. Furthermore, when prepositioning is used, the advanced compression cache on the Cisco WAE is populated, thereby improving performance for users accessing the file if the file has changed since the preposition task.
Prepositioning is helpful in scenarios where large amounts of data need to be transferred, such as software installation files, patch or hot-fix installation files, and antivirus definition file updates. By using prepositioning, enterprise IT organizations can consolidate costly and difficult-to-manage servers that are deployed simply for software distribution (refer to Figure 5).

Figure 5. Cisco WAAS Preposition for Software Distribution Server Consolidation

SUMMARY

Cisco WAAS provides industry-leading file services capabilities that help enterprise IT organizations consolidate costly-to-manage file servers and software distribution servers without compromising the performance that remote-office users have come to expect as a result of many years of working with local infrastructure. With its thorough understanding of the application protocols needed to safely optimize communications, use of file caching to reduce unnecessary data transfers and WAN use, and use of best-in-class WAN optimization, Cisco WAAS provides IT organizations with the tools necessary to simplify, consolidate, and protect remote-office infrastructure.