Dell NetWorker 19.9 Administration Guide

Multiplex backups to Data Domain VTL devices

You can configure multiplexed backups to Data Domain VTL devices on remote, non-dedicated NetWorker storage nodes. Multiplexing is the use of multiple parallel save streams or concurrent sessions to each device. Each additional save stream (max sessions value) to a VTL device reduces the number of devices needed by somewhat less than one because deduplication efficiency decreases slightly.

The following prerequisites, restrictions, and considerations apply:

• NetWorker dedicated storage nodes (DSNs) and NetWorker backup to local VTLs cannot use this configuration.
• Multiplexing decreases deduplication efficiency on the VTLs by 4% to 8% per additional save stream. For example, given a sufficiently large device block size, 4 parallel streams (max sessions=4) results in deduplication ratios that are 12%-24% below the non-multiplexed rate (max sessions=1).
• Deduplication ratios may be initially low when you increase max sessions due to extra processing, following which efficiency improves.
• Heavily used Data Domain systems, with 75% or more disk space already used, can suffer impaired performance when used with multiplexing.
• As a best practice, do not use client-side or server-side encryption during backup to the Data Domain system.