Dell Storage Manager 2020 R1 Administrator's Guide

Handling Hard Links

NDMP backup handles hard link files in the most efficient way by default. That is, the hard link files’ data content will be backed up only once. After the backup operation encounters the first hard link file and backs up its content, the backup process remembers the inode number of that file. Subsequently, when the backup operation encounters files with the same inode number, only the header is backed up. When this backup data stream is restored, the hard link files will be recovered as hard link files.

This mode of backup could create a problem in the case of a selective restore when the selected files or directories to be restored contain hard link files that are not the first instance encountered during backup. In this case, the restore fails and an NDMP message is sent to the DMA server indicating the first instance of the file that should also be included in the selective restore.

To work around this problem, change the behavior during backup. If a backup is started with the DEREF_HARD_LINK environment variable set to Y, the backup will back up all instances of the hard link files as if they were regular files, rather than just backing up the first instance of the hard link files. In this case, a selective restore will always have the file data. The disadvantage of this option is that backups might take longer and more space is required to back up a data set with hard link files.