[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 mirror disk 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 'MirrorDisk' from Resource Type lists and click 'Next' button. When add a resource from the MirrorDisk resource type name, this step will be skipped.
3. Select the source server and mirror volume

4. Chooses a volume of the meta disk.

   The volume of the meta disk needs another seperate volume available to attach a drive letter. The followings need to be prepared for making such volume:

   1. Drive letter
      For example, M

   2. Directory mount
      For example, C:\vdrive
   3. Volume's name in GUID format
      For example, \\?\Volume{ed8a8f02-18b3-11e6-91b4-000c29ac57f8}\
   4. VHD (Virtual Hard Disk)
      For example
        1. m c:\r0_meta.vhd # VHD + format of drive letter
        2. C:\vdrive c:\r0_meta.vhd # VHD + mounting format of a directory
        3. \\?\Volume{ed8a8f02-18b3-11e6-91b4-000c29ac57f8}\  c:\r0_meta.vhd # VHD + GUID method

   
   

   외부 메타 데이터 볼륨

   A meta volume should be created with RAW status that the volume was not formatted, when creating a separate volume. WDRBD accesses to a meta volume as a sector unit basically, therefore, some part of a sector may not accessible because those are protected because of result from request for an authority to write against a boot record area if the volume has been formatted through the particular file system such as NTFS type. Moreover, it would not be able to use as a meta disk for WDRBD because a meta area of the file system such as MFT is made. So it is recommended choosing the option for what the volume is not formatted when creating the initial volume.

   

   
   

   

   [Figure] Mirror Disk Added
   

5. 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
   
   
6. Click the "Finish" button to add the mirror disk resource 

Deleting

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

1. Click the "Delete resource" and a confirming message about deleting resource will appear.
   
   [Figure] Check resource view
   
   
2. Click the "OK" button and a confirming message about deleting the mirror configuration will appear.
   
   [Figure] Deleting mirror disk view
   
   

3.  Click the "OK" button to delete all, or click the "Cancel" button to delete only a DR resource of a mirrored disk configured on MCCS.

State

The following table explains the state of mirror disk resource.

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

Attribute

Show the specified attribute of mirror disk 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.