This function uses to share necessary data for services between cluster nodes which are connected by networks. Mirroring enables a standby server to have the same data as an active server, by replicating data which is accessible from only local point to the standby server through network.
The replication software DRBD9 helps with such mirroring function, and an agent indicates the thing that manages the software.
The agent for mirrored disk manages and registers mirroring configuration for 1:2 replication.
The replication software DRBD9 helps with such mirroring function, and an DR agent for mirrored disk indicates the thing that manages the software.
Table of Contents
It is essential for DRBD9 to be installed in advance, the function of the internal meta data is not available.
[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 DR resource to a group.
- 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.
- Select "MirrorDisk DR" from Resource Type lists and click the "Next" button
Enter the resource name and select Mirror Volume in the cluster.
[Figure] Mirror Disk DR add ScreenTo check configuration information on a remote host which has not been clustered, Click the "More Information" button.
[Figure] Mirror disk DR addition setting screen
- The DR resource of the shared disk is added after clicking the "Finish" button
Deleting
Select the "Resource" → Right click → Delete the resource.
- Click the "Delete resource" button and a confirming message about deleting resource will appear.
- Click the "OK" button and mirror disk is deleted.
The deleted resource will immediately disappear from the management web console.
State
The following table describes MCCS resources' status conversion occurred by state changes or user's commands.
Mirrored disk DR agent: Manages a mirrored disk, and to use this, it is necessary to install a replication program.
| State | Agent command | Description | Note |
|---|---|---|---|
Online It indicates the state that access to a source volume and a writing test is available. | Offline | Changes the current replication state to the Secondary. | |
| Monitoring | <Source Volume> Checks if replication is in the Primary status and data is UptoDate. <Target Volume> Checks if replication is in the Secondary status. | ||
Offline Almost all of states are shown as offline state except for online or error. | Online | Changes the current replication state to the Primary. | |
| Monitoring | Refer to the Description of the Monitoring above. | ||
Fault | Online | Refer to the Description of the Online above. | |
| Offline | Refer to the Description of the Offline above. |
Attribute
Show the specified attribute of Mirror disk DR resource.
Attribute | Description | Type | De-fault | Edit | Note |
| ChkDsk | If this is set to true, it perform the check disk command when the mirror disk is taken online. Before perform this, the mirroring will be automatically paused and this will be resumed after this is completed. | BOOLEAN | false | O | |
| ChkDskArg | It defines check disk command option when Chkdsk is true. /F: Modifies the error in the disk. /R: Recovers the information of damaged sector. (Including /F) | STRING | /F | O | |
| ChkDskTimeout | It is timeout limit to complete or stop the check disk of mirror disk before attaching the disk . If value is '0', MCCS waits to complete the check disk before attaching the disk. | INTEGER | 120초 | O | |
| DirtyBit | There are dirty bits in the source disk. When changed block isn't transmitted to the target disk, this is marked on the block. | BOOLEAN | false | X | |
| Connection | Display the status of connection between the mirror disk's nodes. | STRING | X | ||
| Replication | Display the status of replication between the mirror disk's nodes. | STRING | X | ||
| DiskState | Display the status of disk managed by the mirror disk. | STRING | X | ||
| Resource | Displays the name managed by DRBD | STRING | X | ||
| GI | It is an identifier used to determine whether each household's data copied by the mirror disk is of the latest version. | STRING | X | ||
| MetaDisk | It is the disk where meta data is saved. | STRING | X | ||
| Address | It is an IP address used by mirror disk. | STRING | X | ||
| Port | It is the communication port number used for mirror disk. | INTEGER | 7789 | X | |
| Role | Display the disk role (Primary or Secondary) of the node. | STRING | X | ||
| Device | This is a virtual device name used by mirror disk. | STRING | X | ||
| OutOfSync | Displays whether there is a value of Out Of Sync which needs synchronization. In case it is, the value is true and it also indicates that there is data that synchronization or replication between nodes has not finished. Therefore, failover will be blocked out in case of the true value. | BOOLEAN | false | X | |
| Protocol | It displays mirror type. A = Async mode B = Semi sync mode C = Sync mode | STRING | B | X | |
| Host | MirrorDisk host name of using resource configuration. | STRING | X | ||
| PrimaryPriorityLevel | Indicates a SourceRole Level of each node. The node of the highest value gets the role of Primary. | STRING | 0 | X |
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.
Information on a DR host displays on each attribute as its DR host name.
MCCS has function to limit input values against user's input field, and it provides function detects automatically data which is input wrong by user's mistake.