NDMP Restores are very slow when backups were taken with DAR (Direct Access Recovery)
This article comes from the Netapp article on NDMP File-Level DAR and how it works, and why they can be slow.
This is the process that happens when file level DAR is used:
File level DAR backup
File level DAR restore
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 awhile.