Updating a destination manually

Why to run a manual incremental SnapMirror update

Ordinarily, SnapMirror updates the destination automatically according to the update schedule you specify in the /etc/snapmirror.conf file. However, you can also initiate updates manually with the snapmirror update command. You might need to run an unscheduled update to prevent data loss resulting from a scheduled or threatened power outage or from a destination volume being taken offline for maintenance, repair, upgrade, or data migration. You can also include the snapmirror update command in an external script if you want to drive updates using that script.

How to perform a manual SnapMirror update

To perform an unscheduled SnapMirror incremental update, independent of the schedule in the /etc/snapmirror.conf file, complete the following step.

Step	Action
1	From the destination system, enter the following command: *snapmirror update [options] [dest_system:] {dest_volume* \| /vol/dest_volume/qtree_path}** options can be one or more of the following: `-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` snapshot_name specifies an existing (qtree only) source Snapshot copy to be transferred, rather than a Snapshot copy taken by the source. SnapMirror does not lock or delete this snaphot. snapshot_name cannot be minutely.x, hourly.x, nightly.x, weekly.x, snapshot_for_backup.x or snapshot_for_volcopy.x. You must rename such Snapshot copies on the source and then copy them.

Step

Action

From the destination system, enter the following command:

snapmirror update [options] [dest_system:] {dest_volume | 
/vol/dest_volume/qtree_path}

options can be one or more of the following:

-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 snapshot_name specifies an existing (qtree only) source Snapshot copy to be transferred, rather than a Snapshot copy taken by the source. SnapMirror does not lock or delete this snaphot. snapshot_name cannot be minutely.x, hourly.x, nightly.x, weekly.x, snapshot_for_backup.x or snapshot_for_volcopy.x. You must rename such Snapshot copies on the source and then copy them.

Step	Action
	`-c` snapshot_name creates a Snapshot copy named snapshot_name of a qtree on the destination after the next update (so that it does not compete with any ongoing updates). SnapMirror does not lock or delete this Snapshot copy. snapshot_name cannot be minutely.x, hourly.x, nightly.x, or weekly.x, because these names are reserved for scheduled Snapshot copies. `-S` [source_system:]source_volume \| qtree_path specifies the source system and volume for the update. source_volume is the volume you want to copy. The source specified by the `-S` option must match an entry for source_volume in the /etc/snapmirror.conf file. If one exists but does not match, the operation displays an error message and terminates. If there is no entry for the specified source volume, the command runs. If the `-S` option is not set, the source must be specified in the /etc/snapmirror.conf file. If it is not specified, the operation displays an error message and terminates. dest_system specifies the name of the destination system. dest_volume specifies the destination volume. If it is a scheduled destination of a local source volume as specified in the /etc/snapmirror.conf file, that source volume is assumed to be the source. If the destination volume specified is not in a scheduled relationship, then the `-S` option must be used to provide a source.

Step

Action

-c snapshot_name creates a Snapshot copy named snapshot_name of a qtree on the destination after the next update (so that it does not compete with any ongoing updates). SnapMirror does not lock or delete this Snapshot copy. snapshot_name cannot be minutely.x, hourly.x, nightly.x, or weekly.x, because these names are reserved for scheduled Snapshot copies.
-S [source_system:]source_volume | qtree_path specifies the source system and volume for the update.
source_volume is the volume you want to copy.

The source specified by the -S option must match an entry for source_volume in the /etc/snapmirror.conf file. If one exists but does not match, the operation displays an error message and terminates. If there is no entry for the specified source volume, the command runs.

If the -S option is not set, the source must be specified in the /etc/snapmirror.conf file. If it is not specified, the operation displays an error message and terminates.

dest_system specifies the name of the destination system.

dest_volume specifies the destination volume. If it is a scheduled destination of a local source volume as specified in the /etc/snapmirror.conf file, that source volume is assumed to be the source. If the destination volume specified is not in a scheduled relationship, then the -S option must be used to provide a source.

Example 1

Using the following command, SnapMirror updates the destination (vol2 on systemB) from the source specified in the /etc/snapmirror.conf file:

systemB> snapmirror update systemB:vol2

Example 2

Using the following command, SnapMirror updates the qtree destination on systemB:/vol/vol2/usersbak from the source qtree on systemA:/vol/vol1/users:

systemB> snapmirror update -S systemA:/vol/vol1/users 
systemB:/vol/vol2/usersbak

Creating extra backup Snapshot copies for SnapMirror qtrees

To establish an extra backup Snapshot copy on both sides of a SnapMirror qtree relationship, you can create a manual Snapshot copy using the snap create command and then use the -c and -s options of the snapmirror update command together. These extra backup Snapshot copies can serve as the newest common Snapshot copy in case a base Snapshot copy was accidentally deleted. You can also use them to resynchronize a SnapMirror qtree relationship to an earlier resynchronization point.

Example:

systemB> snap create vol2 my_snap

systemA> snapmirror update -S systemB:/vol/vol2/qtree1 -s my_snap -
c my_dest_snap vol/vol4/qtreeSafe

Result:

You create a Snapshot copy on systemB (the source) called my_snap. Then on systemA (the destination), you update the data in systemA:/vol/ vol4/qtreeSafe from the data in my_snap and store the updated data in the Snapshot copy you create called my_dest_snap. SnapMirror does not automatically delete my_snap and my_dest_snap because they are user-originated Snapshot copies.

What happens after SnapMirror makes incremental updates to the destination

Changes on the source are reflected on the destination after SnapMirror completes the transfer. Changes being copied are not visible during the transfer and are not visible if the transfer is interrupted. After the destination update is finished, you see the changes if you open the file.

SnapMirror automatically deletes old Snapshot copies that are no longer necessary for updating data.