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How is NDMP file history back pressure identified?

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Applies to

  • ONTAP 9
  • NDMP

Answer

  • ONTAP may warn of possible file history backpressure in the backup log, with messages such as:

Warning (Total Dir to FH time spent is greater than 15 percent of phase 3 total time. Please verify the settings of backup application and the network connectivity)

Warning (Total Node to FH time spent is greater than 15 percent of phase 4 total time. Please verify the settings of backup application and the network connectivity)

  • When such warnings are received, it is possible to manually calculate file history statistics, confirming the presence of file history backpressure.

Note: Double-check the units (seconds or milliseconds) to ensure accurate calculations

  1. Check the dump backup log located in /etc/log/backup on the node which hosts the volume being backed up. The interesting logs print after a backup has completed successfully. An aborted or incomplete backup will not provide the logs sufficient to diagnose this problem.
  2. Calculate the duration of phase 3 and phase 4 of the backup in question. In the following example, phase 3 was 20 minutes long and phase 4 was 5 hours long:

dmp Thu Feb 27 12:01:36 CET 2020 /vol/NdmpBackup/(0) Phase_change (III)

dmp Thu Feb 27 12:21:36 CET 2020 /vol/NdmpBackup/(0) Phase_change (IV)

dmp Thu Feb 27 17:21:36 CET 2020 /vol/NdmpBackup/(0) Phase_change (V)

  1. Find the total Dir to FH entry time stats and Node to FH entry time stats for the backup which are presented in milliseconds in ONTAP 9.6 and earlier and seconds in ONTAP 9.7 and later. For example:

dmp Thu Feb 27 17:21:52 CET 2020 /vol/NdmpBackup/(0) Log_msg (Dir to FH entry time stats (msec) numEntries: 2000 min: 0 max: 1526 avg: 5 tot: 15236)

dmp Thu Feb 27 17:21:52 CET 2020 /vol/NdmpBackup/(0) Log_msg (Node to FH Entry time stats (msec) numEntries: 4000 min: 0 max: 1599 avg: 7 tot: 85569)

Note: Make note of the units as these values will be milliseconds "(msec)" in ONTAP 9.6 and earlier and seconds "(sec") in ONTAP 9.7 and later.

  1. If the total Dir to FH entry time is 15% or more of total phase 3 time, this is considered file history backpressure in phase 3. In the above example, 15.236 seconds is only ~1% of the 20 minute phase 3 time, so this is not considered backpressure.
  2. If the total Node to FH entry time is 15% or more of total phase 4 time, this is considered file history backpressure in phase 4. In the above example, 85.569 seconds is <1% of the 5 hour phase 4 time, so this is also not considered backpressure.

Note:

  • In releases prior to ONTAP 9.6, these warnings can be inaccurate due to BUG 1177614.
    • In ONTAP 9.6 and prior, it is recommended to use the above manual calculations to confirm file history backpressure.

Additional Information

FAQ: NDMP File history

 

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