How does file-level Direct Access Recovery (DAR) work?

Applies to

• DATA ONTAP 9.x
• NDMP Backup/Restore

Answer

The process when file-level DAR is used:

• File-level DAR backup

1. The backup software requests the file(s) for the backup job
2. The filer starts the five phases of the backup process. See  NDMP / Dump phases description for more information
3. The information is stored on the internal database of the backup software for later recovery

• File-level DAR restore

1. The filer receives the filename, and the offset map created from the restore
2. The filer seeks through the tape to locate the directory that the file is contained in. This could span the entire tape or even multiple tapes until the offset is reached
3. The entire directory structure is read and compared and selected file is located and restored along with the metadata

• Depending on the number of files in the directory, position of directory and file on the tape, and the number of tapes needing to be read, this process can take a long time to complete.

Additional Information

FAQ: NDMP File history

• The following are two typical applications of file history:

1. Provide a human-readable user interface to backup data
2. Provide a basis for Direct Access Recovery (DAR). DAR allows a DMA to access files / directories directly on tape without having to traverse the entire backup. This allows for quicker file and directory recovery operations.