7-11 Mirror Disk DR
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The Mirror Disk DR resource enables replicate a mirror disk set of a cluster to an off-site DR node for the disaster recovery purpose.
Mirror Disk DR agent act according to mirror disk status and role.
Dynamic information like status and roll of Mirror Disk DR is logged into system event log, this is sent to MCCS by MCCS Event Module.
MCCS Event Module is activated when MCCS service starts.
Data replication component operates by creating mirror set for volumes between two nodes.
Source volume is sit on Primary node, Target volume is sit on Secondary node in a cluster and also off-site DR node.
Client is only available to read/write in the source volume, changed block of the volume is replicated to the target volume through the TCP/IP network connection. At this point, target volume is in lock state and read/write is not allowed. This is to ensure data integrity by preventing the use of target volume.
Mirror Disk DR resource can only register a pre-configured DRBD resource.
Table of Contents
[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.
MCCS for Linux support DRBD which is open source for Mirror disk. Therefore, DRBD should be installed in advance.
The size of disk file system that is created by mirror disk should be created with 128MB
128M space is required to store meta data that manages replication volume service.
Mirror Disk DR resource only support internal meta data type of mirror disk. For more detail about meta data type of mirror disk, please refer to "7.7 Mirror Disk" of this guide.
Mirror IP address should be assigned a virtual IP address between active server and standby server in a primary site. So the virtual IP should be added in a group in advance.
Size of meta data can be changed according to the size of the meta data.
Please refer to DRBD meta data size(Calculation for more details).
When use both DBRB and LVM, only DRBD ON LVM is supported and LVM In DRBD is not supported.
Mirror IP address of the cluster should be assigned a virtual IP address to represent each real IP addresses of both nodes in the primary site. So the virtual IP should be added in a group in advance.
- Select a group → right click → "Add Resource'".
Select "MirrorDisk'" from Resource Type lists and click the "Nex"' button.
Select the mirror volume and MCCS will renewal the information automatically.
The virtual device, mirror IP address and mirror ports will be entered automatically.
If mirror volume is already configured in the volume, "mirrored" will be displayed.
Also, the config data will be entered automatically during the selection, and you cannot change it.
[Figure] Mirror Disk DR Added- Click the "Finish" button to add the mirror disk DR.
Deleting
Select "Resource type" → right click → delete resource.
- Click the "Delete resource" button and a confirming message about deleting resource will appear.
[Figure] Check resource view - 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 status switching of the MCCS resource caused by a user's command and the status.
The command assumes that it is generated by a user.
Mirror disk DR agent: Manages the mirror disk. Copying program should be installed.
| State | Agent command | Description | Note |
|---|---|---|---|
Online In this status, you can access the source volume and perform a writing test properly. | Offline | If the role of mirror resource is online,Unmount (umount) the mirror disk from the mount point and the role of mirror disk demoted to secondary and offline the mirror disk resource. | |
| Monitoring | MCCS consistently handles events of the replication component. | ||
Offline Except for the online and fault states, it is always offline. | Online | Type of operation is determined by the role of the mirror volume at the start node. <Target volume> If the mirror disk is not defined, it is processed as a failure without any operation. | |
| Monitoring | Refer to the description of monitoring as above. | ||
Fault If a writing test failed online, or an attempt to go online is failed, the trouble state is displayed. *Failover deactivation state | Online | Refer to the above online command. | |
| Offline | If the role of mirror resource is online, Unmount (umount) the mirror disk from the mount point and the role of mirror disk is demoted to secondary. |
*If the mirror volume is not defined, It is regarded as the offline state.
Attribute
Show the unique attribute of resource.
Attribute | Description | Type | Default | Edit | Note |
ConnectState | Display the status of connection between the mirror volume's nodes. | STRING | X | ||
| DRConnectState | It shows the connection state of mirror disk of off-site DR node. | STRING | X | ||
| DiskState | Display the status of disk managed by the mirror volume. | STRING | X | ||
| DRDiskState | It shows the state of the mirror disk of off-site DR node. | STRING | X | ||
| DRMirrorIP | It is an IP address of virtual device of MDR. | STRING | X | ||
| DRMirrorPort | It is a port number of mirror disk. | STRING | X | ||
| DRRoleState | It shows the role of the mirror disk of off-site DR node. | STRING | X | ||
| DRTargetIP | It is IP address of off-site DR node for the mirror disk. | STRING | X | ||
| DRVritualDevice | It is the virtual device name using mirror disk of offsite DR node. | STRING | X | ||
| DRSynced | It represents the progress of volume synchronization of off-site DR node. | INTEGER | 0 | X | |
| MDRVolumeName | It shows the name granted to help DRBD managing the mirror disk. | STRING | X | ||
| GI | It is an identifier used to determine whether each household's data copied by the mirror volume is of the latest version. | STRING | X | ||
| GIStatus | It is the status value that compares each node's GI (Generation Identifier) values. | STRING | X | ||
| KillBusyApps | When the mirror resource goes offline, determine whether to forcefully terminate the tasks that refer to the mirror resource. | BOOLEAN | true | O | |
| LastMirrorOnlineTime | Record the system time where the mirror disk went online most recently. | STRING | X | ||
| MetaDisk | It is the disk where meta data is saved. | STRING | X | ||
| MirrorIP | It an IP address used to mirror disk. | STRING | X | ||
| MirrorNetConnectStatus | Display the connection status of the physical mirror network. True: Mirror network connection. (Disconnection by a user's command does not affect the attribute.) | BOOLEAN | true | X | |
| MirrorPort | It is the communication port number used for mirror disk. | STRING | 7789 | X | |
RoleState | Display the volume role managed by the mirror disk. | STRING | X | ||
MountPoint | Display the mount point for the mirror volume managed by an agent. | STRING | X | ||
| MirrorVolume | It is the name of block device actually used by mirror disk. | STRING | X | ||
| MountPoint | It is the directory where the file system can be mounted. If there is no directory or if the directory is already in use, you cannot activate it. | DIRECTORY | O | ||
| OOS | It is the OutOfSync value requiring synchronization. If the value is non zero, it means that there is some data between the nodes not yet replicated or synchronized. | STRING | 0 | X | |
| ProtocolType | This is a data transmission protocol type. A = Async mode B = Semi sync mode C = Sync mode | STRING | B | X | |
| ResyncRate | The ratio of resynchronization between the disk. | INTEGER | X | ||
| RoleState | Display the role of the the mirror disk. | STRING | X | ||
| SB0Policy | If every member within a cluster is secondary, this split-brain recovery policy is automatically executed. | STRING | X | ||
| SB1Policy | If a member within a cluster is primary, this split-brain recovery policy is automatically executed. | STRING | X | ||
| SB2Policy | If every member within a cluster is secondary, this split-brain recovery policy is automatically executed. | STRING | X | ||
SplitBrainStatus | Display the split brain status. True: Split brain occurred. The attributes are valid only if the network disconnection status and GIStatus attributes have the following status values indicating that a split brain occurred. SplitbrainDisconnect The value is set to false, when the split brain is resolved. | BOOLEAN | false | X | |
| Synced | It represents the progress of volume synchronization. | INTEGER | 0 | X | |
| TotalSpace | It represents the total size of the target mirror disk. | INTEGER | 0 | X | |
| UsedSpace | It represents the available size of the target mirror disk. | INTEGER | 0 | X | |
| VirtualDevice | This is a virtual device name used by mirror disk. | STRING | 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.
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.