You might want use SnapMirror to copy a volume from a source storage system to local tape for the following reasons:
Note
The snapmirror store command does not support SnapMirror qtree replication to tape. If you specify a qtree path as the source or destination, SnapMirror returns an error message.
SnapMirror replication to copy data to local tape is meant as an initialization process for SnapMirror relationships and has limitations when used as a backup menthod. Consider the following limitations before using SnapMirror to tape as a backup method.
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.
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.
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.
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.
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.
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.
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.
In this scenario, you want to establish a SnapMirror relationship between a source system and a destination system over a low-bandwidth connection. Incremental Snapshot mirroring from the source to the destination over the low-bandwidth connection is feasible, but the initial base Snapshot mirroring is not. In such a case it might be faster to first transfer the initial base Snapshot image from source to destination via tape, and then set up incremental SnapMirror updates to the destination system via the low-bandwidth connection.
This scenario assumes the following configuration:
Caution
To prevent extended tape-to-storage system transfer time, it is recommended that the destination system disks be the same size and in the same RAID configuration as the source system disks.
You follow this sequence to set up this arrangement:
For more information, see Copying source-to-intermediate tape.
Then, either use the snapmirror update command to manually mirror an incremental update from the source to the destination system over the low-bandwidth connection, or edit the snapmirror.conf file to set up an incremental update schedule from the source to destination system.
For more information, see Initializing a SnapMirror destination via local tape.
To copy a source volume to an intermediate tape, complete the following steps.
| 1 |
If you do not know whether the disk geometries (that is, the size and number of disks) of the source volume and the ultimate destination volume match, use the snapmirror retrieve -g command to determine if this is so. In the consoles of both the source and destination storage systems, enter the following command: snapmirror retrieve -g vol_name For both the source and the destination volume, the system displays the number and block size of the disks it includes. For example, a return value of 7200000x10 7000x10 means that the specified volume consists of 10 disks of 720,000 blocks and 10 disks of 7,000 blocks. |
| 2 |
At the source system, load the tape into a local attached tape device. |
| 3 |
At the source system, start the data transfer to tape by entering the following command: snapmirror store [-g dest_disk_geom] source_volume dest_tapedevices -g dest_disk_geom applies if the disk geometry of the destination volume, as determined in Step 1, is different from the disk geometry of the source volume. If they are different, use the -g parameter to specify the destination volume disk geometry, for example: -g 140000x10,7000x10 source_volume is the volume you are copying. dest_tapedevices is a comma-separated list of tape devices to which you are copying the volume. ResultSnapMirror starts transferring data to tape. This command creates a baseline transfer. If you have to use more than one tape, SnapMirror prompts you for another tape. Example
|
| 4 |
If SnapMirror prompts you for another tape, add another tape to the drive, and continue transfer of data to tape by entering the following command: snapmirror use dest_tapedevices tape_drive dest_tapedevices is the tape device or a comma-separated list of tape devices to which you are copying the volume. tape_drive is the drive holding the new tape you supplied. Note |
| 5 |
Repeat Step 4 until SnapMirror finishes copying the volume to tape. |
| 6 |
Follow the procedure described in Initializing a SnapMirror destination via local tape. |
To initialize a SnapMirror destination volume via local tape, complete the following steps.
| 1 |
Create a volume on the SnapMirror destination system. See the System Administration Storage Management Guide for information about how to create a volume. |
| 2 |
Put the volume in the restricted state. See the System Administration Storage Management Guide for information about how to restrict a volume. |
| 3 |
Load the tape (made with snapmirror store) into the destination system's local tape device. |
| 4 |
Start the initialization by entering the following command on the destination system: snapmirror retrieve dest_volume tape_drive dest_volume is the volume that you are initializing. tape_drive is a tape device or a comma-separated list of devices from which you are restoring the volume. ResultSnapMirror starts transferring data from the tape. If data is stored on more than one tape, SnapMirror prompts you for the next tape. |
| 5 |
If Data ONTAP prompts you for another tape, add the next tape to the drive and restart the initialization by entering the following command: snapmirror use volume tape_list volume is the volume to which you are restoring. tape_list is the tape device from which you are restoring the volume. |
| 6 |
Repeat Step 5 until SnapMirror finishes initializing the volume from the tape. |
| 7 |
If you need to, you can update the data online manually with the following command: snapmirror update [-k n] -S source_system:source_volume [dest_system:]dest_volume -k n sets the maximum transfer speed to n kilobytes per second. This option has the same effect as the kbs argument in the /etc/snapmirror.conf file. -S source_system:source_volume specifies the source system and volume for the migration. source_volume is the volume you want to copy. dest_system is the name of the destination system. dest_volume is the destination volume. For more information about the snapmirror update command, see Updating a destination manually. Note |
After a successful update of the destination system over a connection, you no longer require the source-to-tape SnapMirror relationship and its associated Snapshot copy that you established with the snapmirror store command. To end the source-to-tape backup and delete the Snapshot copy from the source system, complete the following steps.
In this scenario, you use SnapMirror to replicate Snapshot copies from a SnapVault secondary storage system to an attached local tape drive for the purposes of backup. In case of data loss on the SnapVault secondary system, you can restore a specified Snapshot copy back to the SnapVault secondary system.
Note
This scenario applies only to backup of SnapVault secondary storage. Do not apply this configuration for any other purpose.
You need a SnapVault secondary system with an attached local tape drive. The volume on which the secondary storage qtrees reside must also be configured as a SnapMirror source volume.
You follow these steps to set up this arrangement.
For more information, see Copying from a SnapVault volume to local tape.
For more information, see Restoring to SnapVault from a local tape.
To back up a SnapVault volume to tape, complete the following steps.
| 1 |
At the SnapVault secondary storage system, load the tape into a local attached tape device. |
| 2 |
At the SnapVault secondary storage system, start the data transfer to tape by entering the following command: snapmirror store sv_volume dest_tapedevices sv_volume is the volume you are copying. dest_tapedevices is a comma-separated list of tape devices to which you are copying the volume. ResultSnapMirror starts transferring data to tape. This command creates a baseline transfer. If you have to use more than one tape, SnapMirror prompts you for another tape. |
| 3 |
If SnapMirror prompts you for another tape, add another tape to the drive, and continue transfer of data to tape by entering the following command: snapmirror use dest_tapedevices tape_drive dest_tapedevices is a comma-separated list of tape devices to which you are copying the volume. tape_drive is the drive holding the new tape you supplied. Note |
| 4 |
Repeat Step 3 until SnapMirror finishes copying the volume to tape. |
| 5 |
If the volume on the SnapVault secondary system that you backed up ever needs to be restored, follow the procedure described in Restoring to SnapVault from a local tape. |
In event of data loss on a SnapVault secondary storage volume that is also configured as a SnapMirror source, data that has been SnapMirrored to tape can be restored to the SnapVault secondary storage volume with the snapmirror retrieve command.
Note
The snapmirror retrieve command restores only full volumes. If you specify a qtree path as the source or destination, SnapMirror returns an error message.
To restore a SnapMirrored volume on a SnapVault secondary storage system from tape, complete the following steps.
| 1 |
On the SnapVault secondary storage system, use the vol restrict command to put the volume that you want to restore from tape into restricted state. See the System Administration Storage Management Guide for information about how to restrict a volume. |
| 2 |
Load the tape (made with snapmirror store) into the local tape device. |
| 3 |
Start the initialization by entering the following command on the SnapVault secondary storage system: snapmirror retrieve [-h] rest_volume tape_drive The -h option displays the headers of the source tapes but does not transfer data. rest_volume is the volume that you are restoring. tape_drive is a tape device or a comma-separated list of devices from which you are restoring the volume. ResultSnapMirror starts transferring data from the tape. If data is stored on more than one tape, SnapMirror prompts you for the next tape. |
| 4 |
If Data ONTAP prompts you for another tape, add the next tape to the drive and restart the initialization by entering the following command: snapmirror use rest_volume tape_list rest_volume is the volume to which you are restoring. tape_list is the tape device from which you are restoring the volume. |
| 5 |
Repeat Step 4 until SnapMirror finishes initializing the volume from the tape. |
| 6 |
If incremental updates to the baseline Snapshot data that you just restored exist on tape, insert that tape into the SnapVault secondary storage system's local tape drive and enter the following command: snapmirror update [options] [sv_secondary:]sv_volume options can be one or more of the following:
sv_secondary is the name of the SnapVault secondary system that you want to restore to. sv_volume is the volume that you want to restore. For more information about the snapmirror update command, see Updating a destination manually. |
| 7 |
After all tape-to-SnapVault retrieve and update operations are complete, use the snapmirror break command to turn the restored system volume back to completely read-writable status. snapmirror break /vol/volume_name/ |
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Part No. 210-01081_B0
File: mirror29.htm
Last updated: 01-Dec-2005 16:36:03