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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.

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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

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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.

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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.  

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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 "MirrorDisk" from Resource Type lists and click the "Next" button. When add a resource from the MirrorDisk resource type name, this step will be skipped.

3. Enter the resource name.
4. Select the source server and mirror volume, and enter the mount point.

5. The virtual device, mirror ip and mirror port will be set automatically.

   Info
   If mirror disk is already configured on the volume, "mirrored" will be followed next to the volume name. This case you cannot edit the its attributes.

   
   [Figure] Mirror Disk Added
   
   

6. As  the "Additional Settings", Mirror Type option is available and click the "OK" button. Default is Asynchronous Mode Default is "Semi-Synchronization" Mode.
   
   [Figure] Mirror Disk Additional Setting
   
   
7. When click the "OK" button, following warning message will be displayed and click the "OK" button if the informations are correct.
   
   [Figure] Alert popup message after click OK button
   
   
8. Click the "Finish" button to add the mirror disk resource 

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