| PRIMECLUSTER Global Disk Services Configuration and Administration Guide 4.2 (Linux) |
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| Appendix A General Notes | > A.2 Important Points |
In a proxy configuration, by using EMC's TimeFinder and SRDF, the copy functions of EMC's Symmetrix storage units can be used and the synchronization copying between master and proxy can be performed without imposing loads on primary servers or a SAN. In this situation, the storage units carry out copying processes and the processes will continue running even if the server is rebooted.
TimeFinder and SRDF are available to copy data of an entire physical disk to another physical disk, but they are not available to copy data of a disk slice to the other disk area. Therefore, to utilize TimeFinder or SRDF with a proxy configuration, a pair of groups instead of a pair of volumes must be related as a master and a proxy. If a proxy volume instead of a proxy group is specified as a target of the operation to part, rejoin or restore, the operation results in an error, while using TimeFinder or SRDF.
Configuring to meet the following requirements should be done before joining a master group and proxy group.
To utilize TimeFinder:
One of the disks connected to the master group must be the standard device that has been registered with the device group on all of the nodes within the class scope.
A disk connected to the proxy group must be a BCV device that is associated with the same device group as described in 1 on all of the nodes within the class scope.
If the standard device in 1 and the BCV device in 2 are established, the BCV pair must be canceled in advance.
To utilize SRDF:
One of the disks connected to the master group must be the source (R1) device that has been registered with the device group on all of the nodes within the class scope.
A disk connected to the proxy group must be the target (R2) device that is paired with the source (R1) device as above on all of the nodes within the class scope.
The source (R1) device in 1 and the target (R2) device in 2 must be in split status.
Moreover, ensure the following points about management of BCV devices, source (R1) devices and target (R2) devices, which are used with a proxy configuration.
GDS configuration databases cannot be stored in BCV devices and target (R2) devices since the devices are overwritten by data in copy source disks. Therefore, GDS does not regard BCV devices and target (R2) devices as "disks that can be accessed normally" described in "[Explanation]" of "(1) Class becomes closed status during operation" in "Class Status Abnormality."
The BCV and target (R2) devices connected to the proxy group may not be described in the Excluded Device List. However, native devices configuring such devices must be described in the list. For details on the Excluded Device List, see "To Use EMC Symmetrix."
The BCV, source (R1), and target (R2) devices used in a proxy configuration should not be operated using the SYMCLI commands.
If the master and proxy are parted forcibly while copying by TimeFinder or SRDF is in process, a message informing device abnormality is submitted to EMC's customer support center.
When a disk unit's copy function is available, synchronization copying from a master to a proxy is performed using that function. However, the soft copy function (copy function of a GDS driver running on the server) will be used in the following cases.
The soft copy function is specified to be used.
A pair of volumes instead of a pair of groups is related as a master and a proxy.
The configuration of the proxy group to which the data are copied is a mirroring configuration.
The master and the proxy belong to a root class. [Itanium]
A proxy volume with a different physical slice attribute from the master volume is created into a proxy group.
A lower level group is connected to the master group or the proxy group.
A disk of the same size as the disk to which the data are copied is not connected to the master group from which the data are copied.
Disks that constitute the master or the proxy were registered with a class before installing GDS Snapshot.
TimeFinder and SRDF are used for synchronization copying from a master to a proxy after joining or rejoining them, copying for maintaining synchronization, and recording the portion updated while a master and a proxy are parted.
If both TimeFinder and SRDF are available, TimeFinder has precedence over SRDF.
Once the BCV pair or SRDF pair is cancelled, the TimeFinder function or SRDF function is not used.
BCV pairs and SRDF pairs are cancelled when:
Executing [Operation]:[Proxy Operation]:[Restore] in GDS Management View
Using the sdxproxy Cancel command to cancel (break) the BCV or SRDF pair
Using a soft copy function when joining a master and a proxy with the sdxproxy Join -e softcopy command
Using a soft copy function when rejoining a master and a proxy with the sdxproxy Rejoin -e softcopy command
Restoring data from a proxy back to a master with the sdxproxy RejoinRestore command
To make the TimeFinder and SRDF functions available after conducting these operations, break the relationship between the master and the proxy once,remove proxy volumes, and then rejoin the master and the proxy.
To check the modes of the copying in execution, use either:
The [Copy Type] field of the slice information field in GDS Management View
The CPTYPE field displayed with the sdxinfo command
Additionally, the types and the statuses of BCV pairs and SRDF pairs between the master and the proxy can be viewed in the FUNC field and the CPSTAT field displayed with the sdxinfo command.
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