DataKeeper allows mirrors to be created on shared volumes where more than one system has access to the same physical storage. The shared volume can be on the source side of the mirror or on the target side.
Note: Dynamic disks are not supported with Shared Storage because the dynamic disk configuration is stored somewhere (undocumented) on each system, not on the disks themselves. There is currently no way to replicate that configuration between the two systems.
In order to safely create a shared-storage volume resource, the user must ensure that only one system has write access to the volume at any time. This includes the time prior to the creation of the DataKeeper mirror. Since DataKeeper doesn’t know that the volume is shared before a mirror is created, manual steps must be taken to ensure that the volume is never writable on two or more systems at the same time.
To protect the volume from simultaneous write access, use the following procedure. In this example, two systems – SYSA and SYSB – are connected to shared storage, then replicated to a third system, SYSC, the target system. This storage is configured with two volumes which should be assigned drive letters E: and F: on all three systems.
- Power on SYSA, while leaving SYSB powered off.
- Install DataKeeper if it has not been installed.
- Assign drive letters E: and F: to the volumes; format with NTFS if not formatted yet.
- Power off SYSA.
- Power on SYSB.
- Install DataKeeper if it has not been installed and reboot the system after the installation.
- Assign drive letters E: and F: to the shared volumes.
- In a command prompt, run the following commands to set the “shared” config flag:
“%ExtMirrBase%\emcmd” . setconfiguration E 256
“%ExtMirrBase%\emcmd” . setconfiguration F 256
- Reboot SYSB. It will come up with the E: and F: drives locked.
- Power on SYSA. It will come up with the E: and F: drives writable.
- Use the DataKeeper GUI to create a job and mirror from SYSA E: (source) to SYSC E: (target) and from SYSA F: (source) to SYSC F: (target). DataKeeper will detect that SYSB is a shared source system.
An alternative to powering the systems off is to use Disk Management to take the shared physical disk offline.
This procedure can also be used to safely create a mirror on a shared target volume. In the example above, the mirror could have been created from SYSC to SYSA – in that case, the volume SYSB would be a shared target.
If you have more than two shared systems at a site, this same procedure can be used to lock the volume on all systems that will not be part of the initial mirror.