How to specify the options "Follow NFS Mounts" and/or "Cross Mount Points" in a NetBackup policy

Description

When configuring a NetBackup policy, there are two settings to select for controlling how files that reside on mounted file systems will be handled.  These are the "Follow NFS Mounts" and the "Cross Mount Points" settings.  By default, neither of these settings are enabled when creating a new policy. 

• The "Follow NFS" setting controls whether NetBackup will back up or archive any Network File System (NFS) mounts that are named in the backup selection list, or by the user in the case of a user backup or archive.
• The "Cross Mount Points" setting controls whether NetBackup crosses file system boundaries during a backup or archive on UNIX clients, or whether NetBackup enters volume mount points during a backup or archive on Windows clients.  

The following combinations of these settings and the expected behavior are listed below.  The example in each section will reference the following directory structure:

Cross Mount Points: No
Follow NFS: Yes

In this situation any NFS mounted file systems will be traversed during the backup.  However, the backup will not cross mount points to other file systems.  When configuring the backup selections for the policy each NFS mount point must be entered in the backup selections for the policy even if the ALL_LOCAL_DRIVES directive is used.  

For example, the NFS mounted file system /home/nfsuser must be listed specifically in the policy in order to be backed up.  Without the Cross Mount Points setting enabled then NetBackup will not cross from the local file system /home to the NFS file system /home/nfsuser.  

Cross Mount Points: Yes
Follow NFS: No

In this situation backups from one local file system to another will be traversed.  For NFS mounted file systems only the mount point will be backed up.  When configuring the backup selections for the policy do not use the ALL_LOCAL_DRIVES directive.  This can result in the same data being backed up twice.  

For example, if multiple data streams are enabled in the policy then a separate stream could be created for /, /usr, and /home.  The backup stream for / would cross file systems and backup data from /usr and /home.  Additional backup streams for /usr and /home would also be created and the same files would be backed up again.

Note: If the backup selections of the policy specifically lists /home/nfsuser the backup will complete but will only back up the mount point.  Even though the NFS mount was listed specifically the backup will not backup an NFS file system.   If the /home/nfsuser/dir1 is specified then the backup will fail with a Status code 71 (none of the files in the file list exist).  Since the backup will not follow NFS mounts bpbkar will not find any files or directories on an NFS mount point.

Cross Mount Points: Yes
Follow NFS: Yes

In this situation, NetBackup will traverse local mount points as well as include an NFS mount points encountered in the backup.  When configuring the backup selections for the policy, do not use the ALL_LOCAL_DRIVES directive.  

This can result in the same data being backed up twice.  This could also cause any NFS file system be included in the backup

CAUTION: Enabling both of these settings when using the ALL_LOCAL_DRIVES directive is not recommended. This method could potentially allow NetBackup to include file systems that were not intended to be included in the back up. This can severely impact network performance if there are multiple NFS mounts on the system. For example, if an automounted file system /net/projects is mounted when the backup is performed, it will be included in the backup. This could result in gigabytes of unnecessary data being sent over the network and included in the backup.

Other NFS related issues

The following considerations should be taken when backing up NFS mounted file systems.

• Whenever possible, the NFS server should be configured as a NetBackup client and be responsible for backing up the data that resides on the server.  Backing up data from an NFS client will result in the same data being sent over the network twice.  First, from the NFS server to the NetBackup client via an NFS mount and then from the NetBackup client to the NetBackup media server.
• When backing up NFS mounted file systems, the performance of the backup will depend on the speed at which data can be read over the NFS mount.  This can increase the time necessary to back up the client.  The performance can also be impacted if multi streaming is enabled and multiple NFS mounts are being backed up concurrently.
• Using the ALL_LOCAL_DRIVES directive does not include NFS mounted file systems in the listing.  This is normal behavior for NetBackup.  The bpmount command on the client will only report local file systems.  Any NFS file systems will need to be listed specifically in the backup selections of the policy.
• When restoring data to a NFS partition, the NFS file system should be mounted prior to the restore.  If the NFS mount is not available, then the files will be restored to the local file system.