NDMP Backup Formats and Types

The NDMP protocol does not specify a backup data format. The appliance supports three backup types corresponding to different implementations and on-tape formats. DMAs can select a backup type using the following values for the NDMP environment variable "TYPE":

There is no standard NDMP data stream format, so backup streams generated on the appliance can only be restored on 7000-series appliances running compatible software. Future versions of appliance software can generally restore streams backed up from older versions of the software, but the reverse is not necessarily true. For example, the "zfs" backup type is new in 2010.Q3 and systems running 2010.Q1 or earlier cannot restore backup streams created using type "zfs" under 2010.Q3.

NDMP Back up with "dump" and "tar"

When backing up with "dump" and "tar" backup types, administrators specify the data to backup by a filesystem path, called the backup path. For example, if the administrator configures a backup of /export/home, then the share mounted at that path will be backed up. Similarly, if a backup stream is restored to /export/code, then that's the path where files will be restored, even if they were backed up from another path.

Only paths which are mountpoints of existing shares or contained within existing shares may be specified for backup. If the backup path matches a share's mountpoint, only that share is backed up. Otherwise the path must be contained within a share, in which case only the portion of that share under that path is backed up. In both cases, other shares mounted inside the specified share under the backup path will not be backed up; these shares must be specified separately for backup.

Snapshots - If the backup path specifies a live filesystem (e.g., /export/code) or a path contained within a live filesystem (e.g., /export/code/src), the appliance immediately takes a new snapshot and backs up the given path from that snapshot. When the backup completes, the snapshot is destroyed. If the backup path specifies a snapshot (e.g., /export/code/.zfs/snapshot/mysnap), no new snapshot is created and the system backs up from the specified snapshot.

Share metadata - To simplify backup and restore of complex share configurations, "dump" and "tar" backups include share metadata for projects and shares associated with the backup path. This metadata describes the share configuration on the appliance, including protocol sharing properties, quota properties, and other properties configured on the Shares screen. This is not to be confused with filesystem metadata like directory structure and file permissions, which is also backed up and restored with NDMP.

For example, if you back up /export/proj, the share metadata for all shares whose mountpoints start with /export/proj will be backed up, as well as the share metadata for their parent projects. Similarly, if you back up /export/someshare/somedir, and a share is mounted at /export/someshare, that share and its project's share metadata will be backed up.

When restoring, if the destination of the restore path is not contained inside an existing share, projects and shares in the backup stream will be recreated as needed with their original properties as stored in the backup. For example, if you back up /export/foo, which contains project proj1 and shares share1 and share2, and then destroy the project and restore from the backup, then these two shares and the project will be recreated with their backed-up properties as part of the restore operation.

During a restore, if a project exists that would have been automatically recreated, the existing project is used and no new project is automatically created. If a share exists that would have been automatically recreated, and if its mountpoint matches what the appliance expects based on the original backup path and the destination of the restore, then the existing share is used and no new share is automatically created. Otherwise, a new share is automatically created from the metadata in the backup. If a share with the same name already exists (but has a different mountpoint), then the newly created share will be given a unique name starting with "ndmp-" and with the correct mountpoint.

It is recommended that you either restore a stream whose datasets no longer exist on the appliance, allowing the appliance to recreate datasets as specified in the backup stream, or precreate a destination share for restores. Either of these practices avoids surprising results related to the automatic share creation described above.

NDMP Back up with "zfs"

When backing up with type "zfs", administrators specify the data to backup by its canonical name on the appliance. This can be found underneath the name of the share in the BUI:

Figure 11-8  NDMP Share Name

or in the CLI as the value of the canonical_name property. Canonical names do not begin with a leading '/', but when configuring the backup path the canonical name must be prefixed with '/'.

Both projects and shares can be specified for backup using type "zfs". If the canonical name is specified as-is, then a new snapshot is created and used for the backup. A specific snapshot can be specified for backup using the '@snapshot' suffix, in which case no new snapshot is created and the specified snapshot is backed up. For example:

Because level-based incremental backups using the "zfs" backup type require a base snapshot from the previous incremental, the default behavior for level backups for which a new snapshot is created is to keep the new snapshot so that it can be used for subsequent incremental backups. If the DMA indicates that the backup will not be used for subsequent incremental backups by setting UPDATE=n, the newly created snapshot is destroyed after the backup. Existing user snapshots are never destroyed after a backup. See "Incremental backups" below for details.

Share metadata - Share metadata (i.e., share configuration) is always included in "zfs" backups. When restoring a full backup with type "zfs", the destination project or share must not already exist. It will be recreated from the metadata in the backup stream. When restoring an incremental backup with type "zfs", the destination project or share must already exist. Its properties will be updated from the metadata in the backup stream. See "Incremental backups" below for details.