Using VCT for indexing
When Vendor Change Tracking (VCT) is enabled for a D-NAS policy, NetBackup does not perform any file system traversal for indexing a NAS volume. Instead, NetBackup uses the change list from the difference engine of the storage array to perform indexing of files and directories.
D-NAS policy supports the VCT-enabled index backups for NetApp, Dell EMC PowerScale (Isilon), Nutanix Files, and Qumulo NAS arrays.
Index job for the first full schedule:
When the index from snapshot for the first full schedule runs for a NAS volume. Then, NetBackup performs the file system traversal and generates an image catalog file.
File system traversal happens as the array vendors do not have any previous snapshot to get the change list.
Index job for the subsequent full schedule using VCT:
When VCT is enabled in the policy and a subsequent full schedule is run, NetBackup uses the following:
Previous full image catalog.
change list provided by the array vendor's difference engine from NBSM.
Using the previous catalogs, a synthetic catalog is created for the subsequent full schedule.
If number of streams per volume is changed from the last successful full index from snapshot, then NetBackup performs a file system traversal.
Index job for an incremental schedule using VCT:
When VCT is enabled in the policy and incremental schedule runs:
Differential incremental schedule: The change list is identified using the current snapshot and the snapshot of the last successful index job.
Cumulative incremental schedule: The change list is identified using the current snapshot and the snapshot of the last successful full index job.
Following are the file entries that are added to the image catalog for index operation as per the schedule:
Full schedule: The full set of files.
Differential incremental schedule: Files that are added or modified after the last index job run for any schedule.
Cumulative incremental schedule: Files that are added or modified after the index job run for the last full schedule.
For a VCT-enabled D-NAS policy, the Snapshot or Replication retention period in SLP must be greater than the policy's schedule frequency.
VCT is not applicable if the base snapshot is not available.
The expiration period of the previous full and subsequent incremental snapshots is postponed until the next full schedule is completed.
For non-VCT supported arrays, the index job continues to use mount and file system crawl method.