[Figure] Mirroring Configuration

Mirror Mode

Mirror mode employs both asynchronous and synchronous mirroring schemes. Understanding the advantages and disadvantages between synchronous and asynchronous mirroring is essential to the correct operation of this.

Asynchronization Mode

With asynchronous mirroring, each write is captured and a copy of this is made. That copy is queued to be transmitted to the target system as soon as the network will allow it. Meanwhile, the original write request is committed to the underlying storage device and control is immediately returned to the application that initiated the write. At any given time, there may be write transactions waiting in the queue to be sent to the target machine.  But it is important to understand that these writes reach the target volume in time order, so the integrity of the data on the target volume is always a valid snapshot of the source volume at some point in time.  Should the source system fail, it is possible that the target system did not receive all of the writes that were queued up, but the data that has made it to the target volume is valid and usable.

Semi Synchronization Mode 

With semi-synchronous mirroring, each write is captured and transmitted to the target system. Local write completes in the source as soon as the replication packet has reached the target. Normally, no writes are lost in case of failover , but this may can be lost when both nodes are failed simultaneously. 

Synchronization Mode

With synchronous mirroring, each write is captured and transmitted to the target system to be written on the target volume at the same time that the write is committed to the underlying storage device on the source system.  Once both the local and target writes are complete, the write request is acknowledged as complete and control is returned to the application that initiated the write.  With synchronous mirroring, each write is intercepted and transmitted to the target system to be written on the target volume at the same time that the write is committed to the underlying storage device on the source system.  Once both the local and target writes are complete, the write request is acknowledged as complete and control is returned to the application that initiated the write.

Adding

Add the shared disk DR resource to a group.

1. When add a resource from a group name, select a group → right click → "Add Resource". Or select "Edit(E)" from the main menu bar → select "Add Resource". Or select "Add Resource" icon from the tool bar.  
   
2. Select "SharedDisk DR" from Resource Type lists and click the "Next" button. When add a resource from the SharedDisk DR resource type name, this step will be skipped.
3. Enter the resource name and select mirror volume of shared disk in the cluster.
   
   [Figure] Shared Disk DR Resource Added
   
   

4. As the "Additional Settings" button, KillBusyApps option, File System Check options are available and click the "OK" button.

   <killBusyApps>
   When the Shared Disk DR resource goes offline, determine whether to forcefully terminate the tasks that has used the mirror disk resource.
   

   <DoFscK>
   When use this, fsck will be performed when shared disk DR resource is brought online. 

   <FsckOpt>
   Enter the option for fsck.

   
   [Figure] Shared Disk DR Additional Setting

   
   

5. Click the "Finish" button to add the shared disk DR, then VIP address for mirroring will depend to this.
   (For more details about dependency, please refer to '5.4 Dependency Management' of this manual.)

Deleting

Select "Resource type" → right click → delete resource.

1. Click the "Delete resource" button and a confirming message about deleting resource will appear.
   
   
2. Click the "OK" button and mirror disk is deleted. The deleted resource will immediately disappear from the management web console.

State

The following table explains the state of shared disk DR resource.

Shared disk DR agent: Manages a mirror disk, and to use this, it is necessary to install a replication program.

*If the mirror disk is not defined, It is regarded as the offline state.

Attribute

Show the specified attribute of the shared disk DR resource.

Specified attribute values are normally entered when add the resource, This value can be edited or viewed through 'Specified Attribute' table in the Resource Attributes tab on the detailed information panel.