NDMP_BLUEARC_EMBEDDED_HARDLINKS

Backup Administration Guide for Hitachi NAS Platform

Version
15.1.x
Audience
anonymous
Part Number
MK-92HNAS007-29
Possible value Notes
y or n Used to enable or disable inline hard linked file support. Set the value to y to enable, or n to disable. For backups, inline hard linked file support is set to n (disabled) by default, but for multi-stream operations, such as replications and accelerated data copies (ADCs) between servers, the default is overridden and inline hard linked file support is enabled. By default, replication and ADC operations use multiple data streams, so for those operations, inline hard linked file support is used by default.

When enabled, inline hard linked file support causes NDMP to back up hard linked files with both file data and file metadata inline (in a single data stream), which reduces the amount of memory the server needs to manage the data.

Set to n to disable inline hard linked file support, which causes file metadata and file data to be sent in two data streams. Disabling inline hard link file support maintains backup compatibility with older systems or releases.

Inline hard linked file support may not be enabled using the ndmp-option command. Rather, the command used to invoke NDMP must request inline hard linked file support.

Note: Existing programs that can read NDMP data streams for releases prior to release 6.1 will not be able to read backups or recover from backups created using inline hard linked file support.

If a replication fails part way through, it will not be possible to restart replication if the server is downgraded to a release prior to release 6.1.

Using this option with replications and ADCs

When multi-streamed replication or ADC operations are started, this option is enabled. Starting in release 6.1, replication and ADC operations are multi-streamed by default, meaning that this option will be enabled by default for those operations.

Using backups

When backing up a file system:

  • When the embedded hard link option is enabled, the data for each hard linked file is included in the data stream wherever a path to that file is included.

    When enabled, the embedded hard link option increases the amount of data backed up, because multiple copies of the hard linked file data are included. However, it reduces the complexity of managing the backup.

    Also, note that enabling the embedded hard link option reduces the memory requirements needed to keep track of all the hard links.

  • When the embedded hard link option is disabled, paths to hard linked files are included without any data in the main part of the backup and a single copy of the hard link file data is included at the end of the backup.

    This reduces the amount of data backed up, because only a single copy of the hard linked file data is included.

Recommendations for usage with backups

  • If the backup contains many (more than a few hundred thousand) hard linked files, you should enable this option, because it reduces the memory overhead. Note that, where the backup includes many millions of hard linked files, enabling this option may allow the backup to complete where it would not complete if the option is disabled.
  • If the backup contains a relatively small number of hard linked files each containing a large amount of data, you should disable the option.
  • If there is a chance that the backup may need to be restored on an older version of software, you should disable this option.