Administrator Guide

Table 21. Supported NDMP Environment Variables (continued)
Variable Name Description Default
is added to the backup stream during incremental backup so that the
recovery operation can handle files and directories deleted between the
incremental backups.
During backup, if this variable is set, an additional directory listing is added
to the backup data stream. Because of the additional process required, this
addition could affect the backup data stream size and performance.
During recovery, if this variable is set and if the backup data stream was
generated with this variable turned on, the NDMP server handles deleting
files and directories that are deleted between incremental backups.
Setting this variable requires additional processing time and enlarges the
backup data stream size (how much it changes depends on the number of
elements in the backup data set). If this feature is not important to the end
user, it should not be set.
BASE_DATE Used by TSM for token-based backup, as an alternative to using the LEVEL
environment variable.
When BASE_DATE is set to 00, a full backup is performed.
After a full backup completes, a token can be retrieved by retrieving the
DUMP_DATE environment variable. This token can then be passed in later
backups as the value of BASE_DATE. The backup performed in this case is
an incremental backup relative to the time when the token was generated.
When BASE_DATE is set to -1, token-based backup is disabled.
-1
DEREF_HARD_LINK Controls whether hard link files data content are backed up for all
instances of the same file. Valid values are Y and N.
N
Incremental Backups
Each time a backup is performed, the NDMP server stores the timestamp for the backup. When the NDMP server performs an
incremental backup, it uses the timestamp stored for the previous full or incremental backup to determine if a directory or file
needs to be included.
Both supported backup types (dump and tar) support incremental backup. The algorithm for traversing the backup target
directory is the same. However, because inode-based file history generation has different requirements to support DAR, the
backup data stream generated is different:
● dump: Each directory visited will be backed up and a file history entry will be generated. It does not matter whether the
directory has changed.
● tar: Backs up and generates a file history entry only for the directories that have changed.
Therefore, the amount of data backed up using a tar backup will be less than that of a dump backup. The size difference
depends on the number of directories in the backup data set.
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
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FluidFS Administration