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Cisco WAAS Replication Accelerator Mode





Data replication applications are dependent on the IP network infrastructure for their performance. Wide Area Networks (WAN) introduce latency, packet loss, congestion and bandwidth limitations that impact data replication performance. Additionally, WAN links are inefficiently utilized, having to transmit repeated data patterns due to the similarity of data in an organization. Data replication traffic has unique characteristics that require dedicated and specialized resources to expedite processing and overcome the challenges and limitations imposed by the WAN. Data replication traffic is by nature high in volume with a low number of TCP connections. These connections are long lived per session and they are persistent over a long time. This is unlike branch office to data center traffic which is low volume with a high number of TCP connections that are short lived per session.

Replication Accelerator provides the following benefits:

●   Complete data center storage replication jobs into existing or shorter replication windows.

●   Maximize investment in WAN bandwidth for data center storage replication.

●   Meet more stringent recovery point objectives (RPO) at a lower cost.

●   Extend the distance between disaster recovery sites.


Features of Replication Accelerator Mode

  • WAAS RA mode is optimized for High Speed Links, Low Connection Counts, and Low Fan-out.
  • The WAAS replication accelerator mode is optimized for WAN links over 20 Mbps and up to OC-12 (622 Mbps).
  • WAAS Replication Accelerator mode provides increased performance for data replication traffic by providing low latency processing for Data Redundancy Elimination (DRE) as well as further improving TCP Flow Acceleration (TFO) in WAAS.
  • By processing the DRE in RAM and writing to the disk post processing WAAS mitigates disk-processing latency and provides much faster processing while still providing a persistent cache by writing to disk post processing.
  • A WAE device in Replication accelerator mode negotiates optimizations only with like peers configured in Replication Accelerator mode. Only data replication traffic between RA devices is optimized. In most cases RA mode devices will be deployed point to point between data centers and they won't see application traffic, however in cases where users on a Branch Office to DC WAAS configuration are accessing servers in a remote data center and that traffic also passes through the RA mode devices in the DC to DC replication deployment, the application traffic will be passed through by the RA mode devices and optimized by the Branch Office to DC devices only.
  • Application traffic policies (TFO/DRE services) automatically configure once a WAE device is enabled for Replication Accelerator mode. No additional manual configuration is required, unlike with competitors who require manual configuration for this mode of operation.
  • WAAS in RA mode may be deployable in Inline or in redirect mode using WCCP V2. Having both modes allows for installation in any network architecture and offers customers the choice of a simple inline deployment or the resilience and scalability of redirected mode
  • Data-Store Persistence provides for quick recovery and continuation of in process replication in operations by maintaining the cache on the disk. WAAS can leverage the existing cache upon reboot and continue to provide benefit to replication tasks with out having to relearn data patterns.
  • WAAS RA mode provides High-availability through N+1 device clustering in WCCP V2 redirect mode.
  • WAAS RA mode can be managed from the same Central Manager that is managing AA devices. Cisco WAAS 4.1 Central Manager can manage a Replication Accelerator from 4.0.19 version.


Limitations / Restrictions

  • Replication-Accelerator' mode is supported only on WAE-7371 and WAE-7341 running 4.0.19 and above until 4.0.27.
  • Device mode 'Replication Accelerator' can only be configured via CLI
  • As the auto-discovery mechanism distinguishes between WAE running 'Replication Accelerator' mode versus the WAE running 'Application Accelerator' mode the connections between two WAEs running incompatible device mode will not be optimized. Instead, these connections will be established as 'pass-through' connections.
  • Maximum supported DRE fan-out is 9 peers using WAE-7371 and 4 DRE peers using WAE-7341.
  • On WAE-7371 maximum supported concurrent TCP connections are 5000. Similarly, on WAE-7341 maximum supported concurrent TCP connections are 2500.
  • When a WAE's device mode change from 'Application Accelerator' to 'Replication Accelerator' the default policy will be changed as well. So, any changes to existing policy while WAE was in Application Accelerator mode will be lost after the new device mode becomes effect. The same is applicable if a WAE's device mode changes from 'Replication Accelerator' to 'Application Accelerator'.


Cisco WAAS support for Replication Accelerator Mode

Replication Accelerator Mode was introduced in Cisco WAAS 4.0.19 and is available until 4.0.27. It is not included in 4.1 and above versions. For above versions use feature Application Acceleration..


Application Acceleration

The WAAS software comes with over 150 predefined optimization policies that determine the type of application traffic your WAAS system optimizes and accelerates. These predefined policies cover the most common type of application traffic on your network. All application definitions configured in the WAAS Central Manager are globally applied to all WAAS devices that register with the WAAS Central Manager, regardless of the device group membership configuration. The global optimization features determine if TFO Optimization, Data Redundancy Elimination (DRE), and Persistent Compression are enabled on a device or device group. By default, all of these features are enabled. If you choose to disable one of these features, the device will be unable to apply the full WAAS optimization techniques to the traffic that it intercepts.


Deployment Scenarios

As in a Branch Office-to-Data Center (Application Acceleration) scenario, traffic can be intercepted and/or redirected to a WAE that is enabled for Replication Acceleration. This can be done using one of the following methods:

• Inline (Preferred for Replication Acceleration)

• WCCP (N+1 cluster for High Availability and Load Balancing)

• ACE, CSM module, CSS, or similar device


Configuring WAE for Replication Acceleration-Inline mode

To obtain an optimal performance for data replication, it is recommended to use `Inline' mode and installing the WAE that will be performing data replication optimization as close as possible to the storage systems. Thus the WAE that is configured for `Replication Accelerator' will not have to receive non-Data Replication (DR) traffic. The `Inline' mode also supports `Port-Channel', which enables load-balancing and `high-availability' should one of the physical link fails. The following configuration example shows how to enable `Replication Accelerator' mode on WAE.


device mode replication-accelerator   <<<< Enables Replication Acceleration on WAE


interface InlineGroup 1/0

ip address

inline vlan all



Related Information

WAAS Replication Accelerator Mode

Replication Acceleration Deployment Guide

Amir Aziz

It seems that this can only be done by version 4.0.19. Does this mean that I have to downgrade all of my WAEs to use this feature?

Cisco Employee

No Amir,

Post WAAS 4.0 where there is no Replication Accelerator Mode it is generally recommended to use Application Accelerator Mode with the Policy configured for the Replication Traffic as TFO+LZ.  No DRE.



Amir Aziz

Thank Kiran for the info but could you please advise as to how I can configure this policy for Replication Traffic?? Any links??

Cisco Employee

Hi Amir,

This is like any Application Policy configuration, where you can create an Application policy based on the IP address or Port Number and configure the Acceleration Policy to be TFO+LZ.

Please see below the config guide on how to create an Application Policy:

Hope this helps.