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Dell NetWorker 19.9 Administration Guide

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Improving restore performance with multiple threads

Recover workflow for file system backups has been enhanced to perform restores in parallel. This splits recover requests into multiple recover requests resulting in more than one recover stream. This has improved recover performance in comparison to earlier versions. The following recover workflows are supported with devices DD and AFTD:
  • File-by-File restore
  • Save set restore
File-by-file restore:
  • If files are selected from a single saveset , an allocation of maximum four streams is made.
  • If files are selected from multiple savesets less than four, an allocation up to four streams is made. One stream is allocated for each distinct saveset.
  • If files selected from multiple savesets more than four, the split restore logic does not apply as it exceeds the parallelism count; files from each saveset processed together in one stream exceeds the parallelism count.
  • If files are selected from multiple savesets from a single volume, an allocation of one stream per saveset is made.
  • When files are selected from multiple savesets from multiple volumes, an allocation is made based on sessions secured on all required devices. If sessions cannot be assigned for all required devices at the same time, the algorithm falls back to safe mode with a single session against a single volume at a time. This is an existing safety mechanism to ensure recovery can proceed under all circumstances, though not necessarily at the highest possible speed.

Saveset restore: For saveset restore if indexes are online for that particular save set then it applies split restore logic and tries to allocate maximum four recover streams. If indexes are not available for that particular saveset then it reverts back to the old mode of using single stream. As in the file-by-file case, the streams are allocated first at the saveset boundary. This means that if one provides two ssids to be recovered, an allocation of one stream will be made to each of the savesets and the remaining two streams will be used for split restore logic.

This feature is not enabled by default. The user can turn on this feature using "-z" flag using recover command line. To enable from NMC , select the advanced options check box and pass the "-z" flag in the additional command line options. The NetWorker Performance Optimization Planning Guide provides more details on when to turn on the feature.
NOTE:

NDMP and BBB backup types are not supported for parallel restore. Tape, VTL, CloudBoost, and DDCT device types are not supported. The Recover feature is not supported using WinWorkr GUI application.

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