NetWorker: How to Configure Token Based Backups for NDMP Clients

Token Based Backup (TBB) for NDMP and NAS clients is a method for specifying and performing INCR backups using NDMP. The traditional incremental backup type for NDMP clients is using FULL and LEVEL [1-9] backups. However, LEVEL backups are limiting as only nine levels of consecutive incremental backups can be done before a cumulative or FULL backup must be specified. With TBB, depending on NAS filer type, a theoretically infinite number of INCR backups can be done in between FULL backups.

TBB works by the exchange of 'tokens' between NetWorker and the NDMP client during the backup. The tokens are BASE_DATE and DUMP_DATE and they are calculated numerical values based on time stamp and incremental backup sequence for the particular save set.

BASE_DATE is the token generated by NetWorker at the start of the TBB backup. NetWorker passes the BASE_DATE token to the NAS to a.) tell the NAS it can support TBB and b.) indicate the token (time stamp) which the NAS must reference in order to generate a list of files that have changed and need to be backed up incrementally. BASE_DATE=0 is a special token value that indicates a FULL backup is to be performed. BASE_DATE=0 is specified automatically if there is no previous FULL backup of the save set or by the FULL schedule set by the NetWorker system administrator.

DUMP_DATE is the token generated by the NDMP client (NAS filer). The DUMP_DATE token is created at the end of the backup and is sent to NetWorker to be recorded in the media database along with the other NDMP save set attributes. The DUMP_DATE is calculated based on the save time of the backup and the incremental backup sequence.

The DUMP_DATE token from the last save set is used by NetWorker to calculate the new BASE_DATE token to send to the NAS for the next INCR backup. At the end of that backup the NAS generates a new DUMP_DATE token and sends it back to NetWorker with that save set, and so on. This exchange of tokens between NetWorker and the NDMP client device continues for as long as TBB is enabled and FULL and INCR backups are designated in the client schedule. The BASE_DATE and DUMP_DATE tokens for each NDMP save set are save set attributes and can be viewed using the mminfo query:

mminfo -aS -q ssid=[ssid]

Enable Token Based Backup

• In the NetWorker Management Console (NMC), edit the NDMP or NAS client.
• In the Application Information field, set the following variable:

  USE_TBB_IF_AVAILABLE=Y

• This variable is set automatically when creating an NDMP client using the New Client Wizard.
• Save the client configuration.
• Configure the client schedule to use FULL and INCR backup types.

Disable Token Based Backup

• To disable TBB, edit the client and set the variable to:

  USE_TBB_IF_AVAILABLE=N

• Change the client schedule to use FULL and LEVEL 1-9 backup types instead of INCR.
• Disabling TBB is useful for troubleshooting or when LEVEL backups are preferred.

Although, theoretically, an infinite number of INCR backups may be performed between FULL, this is not realistic in practice. The load on the NAS and NetWorker increases with each INCR backup and too many INCR backups between FULL can significantly affect RPO and RTO. For best performance and efficiency NetWorker recommends no more than 28 consecutive INCR backups between FULL.

With TBB enabled, both, INCR and LEVEL [1-9] backups may be specified in the client schedule (NetWorker does not preclude this configuration). However, due to unreliable/unexpected behavior by the various NAS filer types, it is recommended to avoid mixing INCR and LEVEL backups of the same save set in NetWorker. Either enable TBB and specify FULL and INCR backups only or disable TBB (USE_TBB_IF_AVAILABLE=N) and specify FULL and LEVEL [1-9] backups only.

TBB functionality and implementation is defined by the NDMP v.4 standard and is adhered to by NetWorker for all NAS filer types that support TBB and have been qualified with NetWorker, i.e. NetWorker does not do anything proprietary in its implementation of TBB. Moreover, NetWorker qualification of the NAS filer specifically for TBB is required before TBB can be enabled. Thus, a NAS filer that may otherwise support Token Based Backups may still not work with NetWorker TBB (refer to the NetWorker NDMP User's Guide for a list of supported devices).

In the event that the NAS filer does not support TBB all INCR backups will run as FULL instead. In that case, the only option is to specify LEVEL [1-9] incremental backups. If the NAS filer does support TBB but has not yet been qualified with NetWorker and is not on the list of supported TBB filers the support limitation *may* be bypassed using the override variable ATTEMPT_TBB=Y ('Application Information' variable).