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Manual Chapter: Deduplication
Manual Chapter
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What is symmetric data deduplication?

WAN Optimization Manager™ (WOM®) uses symmetric data deduplication to reduce the amount of bandwidth consumed across a WAN link for repeated data transfers. This feature is available only with a WOM license.

With data deduplication, the system performs pattern matching on the transmitted WAN data rather than caching. If any part of the transmitted data has already been sent, BIG-IP WOM replaces the previously transmitted data with references. As data flows through the pair, each WOM records the byte patterns and builds a synchronized dictionary. If an identical pattern of bytes traverses the WAN more than once, the BIG-IP WOM nearest the sender replaces the byte pattern with a reference to it, compressing the data. When the reference reaches the other side of the WAN, the remote BIG-IP WOM replaces the reference with the data, restoring the data to its original format.

Symmetric data deduplication provides the greatest benefit when transferring objects greater than 32K.

Enabling symmetric data deduplication

Ensure that you have licensed and provisioned WAN Optimization Manager™ (WOM® on the BIG-IP® system.
Symmetric data deduplication reduces the amount of bandwidth consumed across a WAN link. You can enable symmetric data deduplication on the iSession™ connection between the local endpoint and any remote endpoints.
  1. On the Main tab, expand WAN Optimization and click Symmetric Deduplication.
  2. In the Maximum Number of Remote Endpoints field, type the number of BIG-IP WOM systems that you expect to connect to this one. This number specifies the maximum number of remote endpoints that can have symmetric data deduplication enabled, and thus, share the available cache. Any added WOM remote endpoint that exceeds this number receives no cache for deduplication.
  3. For the Enable Symmetric Deduplication setting, select Yes.
  4. Specify the method of storage for symmetric data deduplication.
    Option Description
    Disk Specifies that WOM uses the disk, in addition to memory, for storing information used for optimization.
    Note: If you enable data storage on the disk, you must then restart the datastor service from the command line using the command sequence bigstart restart datastor.
    Memory Specifies that WOM uses only memory for storing information used for optimization.
    Note: This setting can provide benefits for higher speed links.
  5. Click Update to save changes.
    Important: Updating any of these settings causes the deduplication cache to clear.
Symmetric data deduplication starts after an iSession connection is established with a remote endpoint that also has symmetric data deduplication enabled, as long as the number of remote endpoints does not exceed the value in the Maximum Number of Remote Endpoints field.

Disabling symmetric data deduplication

You can disable symmetric data deduplication on the iSession™ connections between the local endpoint and any remote endpoints.
  1. On the Main tab, expand WAN Optimization and click Symmetric Deduplication.
  2. For the Enable Symmetric Deduplication setting, select No.
  3. Click Update to save the change.
Symmetric data deduplication stops on all iSession connections between the local endpoint and any remote endpoints, and the deduplication cache clears.

What is deduplication cache?

Deduplication cache is the location to which WAN Optimization Manager™ (WOM®) copies data that it has previously transferred. The system creates a deduplication cache area for each pair of BIG-IP WOM systems that are set up to optimize traffic between them. Both systems keep the information in the deduplication cache synchronized between the endpoints on the two BIG-IP WOM systems. If the same or similar information is requested again, the system can send the optimized version of the data instead of sending it in its entirety.

The Remote Endpoints list screen identifies the deduplication cache as SDD (symmetric data deduplication) cache and displays the amounts apportioned to the listed endpoints.

Determining the size of deduplication cache

The following factors determine the size of deduplication cache on BIG-IP® WOM®.

Factor Description
BIG-IP WOM platform Memory and disk sizes vary for different hardware platforms, and these specifications determine the maximum size that the system can reserve for deduplication cache.
Module provisioning If more resources are provisioned for BIG-IP WOM, more can be used for deduplication cache.
Disk or memory mode The size of deduplication cache varies significantly, depending on whether you are storing it on disk or in memory.
Number of remote endpoints The total size of deduplication cache divided by the maximum number of remote endpoints yields the amount of deduplication cache that a WOM assigns to its local and remote endpoints.
Size of cache on remote endpoints The local endpoint negotiates with each remote endpoint to determine the amount of cache available. For each pair of BIG-IP WOM systems, the smaller amount is used for both endpoints on that connection.

Clearing the deduplication cache

Under some circumstances, you might want to clear the deduplication cache. If you are testing the performance of symmetric data deduplication, you might want to clear the cache before you start and reset statistics, to ensure accurate performance data.
  1. On the Main tab, expand WAN Optimization and click Remote Endpoints.
  2. In the Remote Endpoints List screen, select the check box next to the remote endpoint for which you want to clear the cache, and then click Clear Dedup Cache.
    Note: Make sure you select a check box. If you do not select a remote endpoint, the system does not clear any deduplication cache.
The system clears the deduplication cache that it reserves for the remote endpoint you select. The system communicates to the remote endpoint that the deduplication cache is clear, and the remote endpoint clears its deduplication cache for traffic from this local endpoint, as well. Therefore, you need only clear the cache on one BIG-IP® WOM® in a pair, not both.
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