The shared disk DR resource manages data copying between the shared volume and the remote server.

The shared disk DR resource is composed of three servers that manage the shared volume. MCCS is only operable at the server that composes the shared volume.
In other words, MCCS does not operate at the remote server. MCCS is not involved with operation of the remote server, so, administrators need to perform manual operation or register necessary actions for processing in advance.

Data is copied from the server with the source volume to the server with the target volume. Now, the other source server that cannot access the shared volume recognizes the shared volume as the one having the "NONE" role.
Thus, the target volume and the "NONE" volume are locked and you cannot write or read to and from them. The goal is to prohibit the use of the corresponding volume so that the data integrity can be guaranteed.

Major content of this page

[Figure] Mirroring Configuration

Data sync

Mirroring is classified into a sync mode and an async mode depending on the time of response to a request for saving.

Async mode

A response to writing on the mirror disk is immediately sent after the source volume is saved. Since it does not wait until data is sent to the target volume and saved there, the response time is very fast. However, in case of trouble, it can cause data mismatches due to data failed to be transmitted at that time.

Sync mode

When there is a request for writing to the disk, it will be written to the target volume as soon as it is written to the source volume. The final, successful response to a request for writing is achieved after both the source and the target volume are written. The response time is slow, but there exists the same data for the source and the target all the times.

Add

Add the DR shared disk resource. Before you can add the shared disk DR resource, you must install a copy tool at the remote server that data will be copied to.

Select the group -> Right click with the mouse -> Add the resource.
In resource wizard, select a shared disk DR and click the Next button.
The shared volume set of resource wizard will display the drive characters that can be used to compose the shared disk DR and the existing drive characters that are already configured.
You cannot inquire about information at the remote server. So, you need to enter IP addresses on your own.

The drive letter to be used as the shared disk DR should be same on the both nodes in a cluster. Data will be replicated to the off-site DR node(Remote server) from the source node. The remote server cannot be the source. Be careful when you select the drive letter where data exists in the remote server, the data will be overwritten when mirror set in completed. If you try to add an existing mirror disk between shared disk set and remote disk, <mirrored> will be follwoed to the driver letter of shared disk.

[Figure] Shared Disk DR Resource Added
Click the 'Additional Setup' to define the synch mode and the disk test option.

<Sync mode> Once selected, the sync mode cannot be reversed. So, be careful.
Sync mode : Response is slow but there is no data loss involved. Async mode : Relatively faster than the sync mode but it can suffer from data loss.
<Disk test option> Set the disk test command option. For more details on the function, refer to MSDN.

[Figure] Shared Disk DR Additional Setting
Press the Finish button after adding the shared disk DR resource, the following warning screen will be displayed.
Check again if it is the correct source server selected.
If not, then click on the 'Cancel' button and set it again.

[Figure] The warning screen displayed when you press the Finish button after adding the shared disk DR resource
Click the 'Finish' button to add the shared disk DR resource. You can immediately check the result in the management web console.

Delete

Select the resource -> Right click with the mouse -> Delete the resource.
The deleted resource will immediately disappear from the management web console.

Status

The following table explains the status changing of the MCCS resource caused by a user's command and the status.
The command assumes that it is generated by a user.

Shared disk DR agent: Manages the mirror disk. Copying program should be installed.

Status	Agent's functions	Description	Note
Online In this status, you can access the source volume and perform a writing test properly.	Offline	Regardless of the mirror role, the LOCKVOLUME command is used to lock the volume. If the mirror disk is not defined, the LOCKVOLUME command is ignored and regarded as a failure.
	Monitoring	Before monitoring, update the status of resource first. Perform a disk write test to determine the status of resource. If the writing test is successful, it is regarded as the online state. If the writing test failed on the disk, it is regarded as the offline state.
Offline Except for the online and trouble states, it is always offline.	Online	Type of operation is determined by the role of the mirror disk at the start node. <Source volume> 1. You can unlock and write the volume. 2.To unlock, you can use the 'UNLOCKVOLUME' menu in the copy program. Check whether there are dirty bits. <Target or NONE volume> 1. If the mirror role is target or NONE volume, run the SWITCHOVERVOLUME command.
	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 When a mirror network communication failure, target node or target disk failure occurs, the mirror state is changed from 'MIRRORING' to other, such as 'MIRROR_PAUSED'. If the mirror status is not 'MIRRORING', a failover will take place and it can cause data losses or damages. To prevent this problem, an agent deactivates the failover mode if the mirror status is not "MIRRORING". If the failover mode is deactivated, no failover will take place even if manual failover or troubles occur. If mirror network has been failed and then, recovered as normal, mirror status is changed to RESYNC and data re-synching is initiated between primary cluster set and off-site DR node. When the mirror status is changed to MIRRORING, the failover mode will be also automatically activated.	Online	Refer to the above online command.
	Offline	Regardless of the mirror role, the LOCKVOLUME command is used to lock the volume. If the mirror disk is not defined, the LOCKVOLUME command is ignored and regarded as a failure.

Attribute

Show the unique attribute of the shared disk DR resource.

ArgList Factor	Description	Type	Default	Modification	Note
ChkDsk	When the volume is mounted, according to the 'Disk Test Options', disk is tested for errors. If it is set to true, and if dirty bits are set to the online volume, the ChkdskArg option will be used to run checkdisk. Before running checkdisk, the mirror copying will be automatically stopped and resynchronization will be performed after finished.	BOOLEAN	false	O
ChkdskArg	When the checkdisk (Chkdsk) option is set to true, the check disk command option is activated.	STRING	/F	O
DirtyBit	It means that dirty bits are set to the target mirror disk. In general, if you need to check the integrity of the target volume, the system will set this.	BOOLEAN	false	X
DriveLetter	The mirror disk is assigned to the drive letter. It should be configured to obtain the same value at the source and the target systems.	STRING		X
DRState	The mirror status of the mirror disk. It is renewed from an event log.	STRING		X
DRType	Determine the mirror synchronization mode. Set it to A or S. ( A - async mode, S - sync mode) * If it is set to asynch mode, data loss can occur.	STRING	A	X
ResyncNeed	It represents the total sum of the blocks requiring re-synchronizing.	INTEGER		X
ResyncTotal	It is the total sum of the re-synchronizing blocks.	INTEGER		X
SharedSrcIp	It is the IP address used to manage the volume shared between two nodes.	STRING		X
SharedSrcRole	It shows the role of the shared disk for each node.	STRING		X
TargetDRIp	It is IP address of off-site DR node for mirror disk.	IP ADDRESS		X
TargetDRLetter	It is a driver letter using mirror disk of off-site DR node.	STRING		X
TargetDRRole	It shows the role of mirror disk of off-site DR node.	STRING		X
TotalSpace	It represents the total size of the target mirror disk.	INTEGER		X
UsedSpace	It represents the available size of the target mirror disk.	INTEGER		X

Attribute value of ArgList arguments are the values that are added resources and the value can be changed or viewed through ’Specified Attribute’ list on the detailed information panel.

MCCS 4.1 English Online Help

7.11 Shared Disk DR

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