| Disk geometry |
When SnapMirror replicates data to tape, it optimizes writing of the file system based on the disk geometry of either the source or destination file system.
The disk geometry of the source file system is used by default, but you can specify the disk geometry of the destination file system using the snapmirror store -g command.
See the na_snapmirror(1) man page for more information.
If you retrieve a backup tape into a file system that does not match the disk geometry of the storage system used when writing the data on to tape, the retrieve can be extremely slow.
Note: If FlexVol volumes are in place, disk geometry mismatch when restoring the volume is not an issue.
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| File system version |
Data written to tape is a block by block copy of the file system associated with a particular version of Data ONTAP; therefore, when you retrieve data from tape, the destination of the retrieval must use the same or later version of Data ONTAP used when storing data to tape.
If you attempt to retrieve data to a destination that uses an older version of Data ONTAP, the retrieval will fail. |
| Snapshot copy issues |
Because the intended purpose of SnapMirror to tape is to initialize mirrors for SnapMirror relationships, it maintains Snapshot copies that future SnapMirror relationships use to perform updates. When used as a backup method, Snapshot copies are created, but never used; therefore, Snapshot copy and data resources are wasted.
Note: You can manage and delete Snapshot copies using the snapmirror release and snapmirror destinations commands. See the na_snapmirror(1) man page for more information.
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| Volume types |
The traditional volume file system format is different from the FlexVol volume file system format.
Because of this difference, a backed up FlexVol volume cannot be retrieved on a traditional volume. Likewise, a backed up traditional volume cannot be retrieved on a FlexVol volume. |
| Lack of archive support |
Some backups are made to be kept for a long time; as such, they become long term storage of old versions of data. Backups using SnapMirror replication to tape are in a format that is only readable by Data ONTAP and the WAFL file system, and is not meant for long term storage. Keeping a set of tapes for extended periods of time risks the ability to restore them in the future. |
| Effects of a bad tape |
When retrieving a file system from tape, the format of the SnapMirror replication to tape requires the entire file system to be retrieved before the file system is usable. A bad tape when retrieving a file system means that not all of the file system is retrievable; therefore, the file system is not constructible and all of the data is unavailable. |
| Lack of backup features |
Using SnapMirror replication to copy data to tape does not have features that backup software does. For example, features like individual file restore, backup indexing, and incremental backups are not supported. |
