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Using SnapMirror

Using SnapMirror with LUNs  Top

You can use SnapMirror to replicate WAFL volumes or qtrees containing LUNs. A qtree is a special subdirectory of the root directory of a volume.

Snap Mirror destination WAFL volumes and qtrees are read-only, which means that LUNs can be listed using the lun show command on the destination filer.

To set up SnapMirror to back up LUNs and then make the LUNs writable so that you can export them, complete the following steps.

Step

Action
1

Make sure that you followed the procedures in the Data ONTAP 6.4 System Administration Data Protection Guide for

  • Preparing to run SnapMirror
  • Specifying the destination filer on the source filer
  • Creating or editing the /etc/snapmirror.conf file
  • Starting SnapMirror

    Caution
    You must save contents of host file system buffers to disk before running snapmirror commands on the filer.
2

From the destination filer, enter the following command.

snapmirror initialize [options] [dest_filer:] 
{dest_volume | qtree_path}
Example: 
snapmirror initialize 
host1:/vol/vol_name/qtree_1 filerA:/vol/vol_name/qtree_1

Note
If you need to update the snapshot at a time not specified in the snapmirror.conf file, use the snapmirror update command. See complete information in the SnapMirror chapter of the Data ONTAP 6.4 Data Protection Guide.

Recovering LUNs from the SnapMIrror destination  Top

You can see the LUN residing in SnapMirror destination volumes or qtrees using the lun show command. You cannot map or export these LUNs to other hosts, however, until you use the mirror break command to make the qtree or volume writable.

For qtree-based SnapMirror, you can create a writable LUN outside of the read-only destination qtree instead of having to break the mirror, which enables you to take backups while continuing to mirror the source qtree.

Note
In Data ONTAP 6.3 and later, WAFL volumes can be "space reserved," which means that if free space within the WAFL volume is below a certain threshold, snapshots cannot be taken and SnapMirror transfers can fail.

To recover data from a LUN that resides in a SnapMirror destination, complete the following steps.

Step

Action
1

Enter the following command to see the LUN backup that you want to recover:

lun show
Result

Data ONTAP shows all the LUNs on the filer on which the command is run.

Example

backup_server> lun show

  /vol/vol0/qtree1/lun1                 2g (2147483648)

  /vol/vol0/qtree1/payroll_backup_lun   1g (1073741824)
2

Make the WAFL volume or qtree writable so that it can be accessed or exported by entering the following command:

snapmirror break {volume_name | 
/vol/volume_name/qtree_name}
Example

snapmirror break 
/vol/vol_name/qtree_1/payroll_backup_lun
3

Export the LUN to the administrative host (if that is where you want it) by entering the following command:

lun map /vol/vol_name/qtree_name
Example

lun map /vol/vol1/qtree_1/payroll_backup_lun server 3
4

Create a new LUN in the active file system from the existing snapshot so that it is writable by entering the following command:

lun create -b <snapshot lun-path> <lun-path>

Note
SnapDrive is tightly integrated with SnapMirror and creates application-consistent snapshots that can then be replicated by SnapMirror. See the SnapDrive 2.0 Installation and Administration Guide.

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Last updated: 01/17/03 17:40:37