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What is a Block Ownership Calculation Scanner?

Last Updated:

Applies to

  • Clustered Data ONTAP
  • Data ONTAP 7-Mode


The   wafl scan status  command reports a block ownership calculation scanner and the storage system experiences a slight to extreme performance issue when this command is run.

If this is causing a performance impact, work to identify the root cause. Alternatively, a fix for BUG 767795, which requires Data ONTAP 8.2.1 or later, can also reduce the impact felt by the scanner.

Also the linked BUGs 698798, 821320, and 648017 bring further improvements. However, this is a normal process if a product similar to the ones below is used.

The Write-Anywhere File Layout (WAFL) file system has many background processes that take place when the system is idle. It helps keep the system optimal and reduces other issues or disruptions. One of these is called ' block ownership scanner '. When the snapshot delete command is run through CLI or some other form, or another snapshot operation is ran, WAFL runs the ' block ownership calculation ' scanner to obtain an approximation of block ownership changes.

This can be performed by:

  • DataFabric Manager (DFM)/OnCommand Unified Manager
  • Some versions of OnCommand System Manager
  • SFSR (Single File Snap Restore)
  • User manually copying a file from the .snapshot directory back to the active
  • filesystem using NFS.
  • Brute force WAFL scanner invocation from the command line
  • Brute force WAFL scanner invocation from a browser (ZAPI)
  • Other commands that scan changes between snapshots, like ' snap delta '

Perform the following steps to see where the block ownership calculation scanner is coming from:

1. On the Data ONTAP 7-Mode storage system, run options auditlog.readonly_api.enable on .
On clustered Data ONTAP, run the   ::> security audit modify -ontapiget on  command.

2. Run the command rdfile /etc/log/auditlog.log for Data ONTAP 7-Mode or on the node shell and look for the line containing snapshot-delta-info or snapshot-list-info .

3. If you use NetApp Management Console/DFM/OnCommand Unified Manager 5.x, see below to reduce the frequency of the scanners.

Perform the following steps to help reduce ZAPI calls for OnCommand Unified Manager/DFM 5.x or earlier:

1. SSH into the DFM server if Linux based or RDP into it if Windows based and open a command prompt as administrator (Start > cmd > right-click, and click Run as Administrator, then accept the UAC prompt.

2. From the CLI, run the following commands:

dfm option set snapmirrorMonInterval=12hours
dfm option set snapshotMonInterval=12hours
dfm option set dsConformanceMonInterval=12hours
dfm option set snapDeltaMonitorEnabled=no
dfm option set isEnableWGChecks=no

Additional Information


NetApp provides no representations or warranties regarding the accuracy or reliability or serviceability of any information or recommendations provided in this publication or with respect to any results that may be obtained by the use of the information or observance of any recommendations provided herein. The information in this document is distributed AS IS and the use of this information or the implementation of any recommendations or techniques herein is a customer's responsibility and depends on the customer's ability to evaluate and integrate them into the customer's operational environment. This document and the information contained herein may be used solely in connection with the NetApp products discussed in this document.


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