Date: Jan 2008
Product & Version: All NetVault: Backup versions
OS Version: All
Module & Version: All NDMP Plugin versions
Application version: Ontap
Symptoms: When using the NDMP plugin to back up volumes on a filer that are SnapMirror volumes, the filer's root volume fills up.
Reason: This may be a result of backups of a snapmirror destination volume via NDMP. Because the NetApp filer can't write the DAR table to the read-only snapmirror volume, it writes this information in the root volume instead.
Solution: In order to enable enhanced DAR, the filer tracks additional information. If this is disabled, the filer will stop writing this information and consequently will stop filling up the root volume. This is disabled by setting the NDMP option ndmpd.offset_map.enable to false.
According to NetApp, enhanced DAR is necessary for "Directory DAR, DAR for files with NT Streams, more optimized DAR & support". Traditional DAR will still be available, but restore performance and functionality will be affected.
Alternatively, you might want to look at using the SnapMirror-to-Tape plugin to backup the entire SnapMirror images instead of backing them up through the NDMP plugin, which requires additional file information and history for browse and restore (and uses DAR and enhanced DAR to speed this up).
Please refer to the text above