Mirror pubsets, in other words pubsets in which the pubset volumes are subject to data mirroring, are supported by VM2000 for assigning and releasing pubsets. The actions of VM2000 depend on the type of data mirroring.
Dual Recording by Volume (DRV)
DRV is a recording method in BS2000 which enables the data to be stored in duplicate on two disks, see the “DRV” manual [5]. Depending on the operating mode, DRV is used to record data of a logical disk on one physical disk (mono mode) or on two physical disks (dual mode). DRV is not involved in conventional SRV mode (Single Recording by Volume).
When a disk is operated in mono mode (or in SRV mode), the required VM2000 function is executed only for the one device when the *PUBSET-DEVICES operand is specified for this logical disk. The disk device which is physically available or entered in the MRS catalog must be specified as the pubres device. The device attributes PUBRES-FOR-ASSIGNMENT and PUBRES-FOR-ATTRIBUTES are displayed for the pubres device when /SHOW-VM-DEVICE-STATUS is used, see "Assigning and removing pubsets of a VM".
When a disk is operated in dual mode, the required VM2000 function is executed when the *PUBSET-DEVICES operand is specified for both devices of the logical DRV disk concerned. Either of the two DRV disk devices can be specified or entered in the MRS catalog as the pubres device. The device attributes PUBRES-FOR-ASSIGNMENT and PUBRES-FOR-ATTRIBUTES are displayed for both pubres devices when /SHOW-VM-DEVICE-STATUS is used, see "Assigning and removing pubsets of a VM".
If the DRV configuration changes, e.g. because of a switch from dual to mono mode, the failure of a disk or the resumption of dual mode, this does not immediately result in the pubset device list being changed in the SVL of the pubres device(s). In this case a VM2000 command for the pubset is still effective for the pubset’s “old” device list. The pubset device lists are changed only when one of the pubsets is exported or imported or in the event of dynamic pubset reconfiguration, see "Pubset reconfiguration".
Mirror disks in the local disk storage system
Clone units are additional local mirror disks in external disk storage systems which can be split for other purposes without impairing ongoing input/output operations. See the “SHC-OSD” manual [20].
The following procedure applies for clone units in VM2000:
When a pubset with clone units is operated, the required VM2000 function is executed on the pubset’s original units when the
*PUBSET-DEVICESoperand is specified, provided the original unit was specified for the pubres device or is entered in the MRS catalog (normal case).In exceptional cases one of the pubres device’s clone units can also be specified. The required VM2000 function is then executed on the set of the pubset’s clone units which belongs to the specified clone unit of the pubres device. In this case the software product SHC-OSD is also required in the monitor system.
The (first) access of SHC-OSD to the configuration data of an external disk storage system can take a few minutes. In this case the VM2000 command is aborted with a timeout (messageVMS4252). The VM2000 command should be retried later. The required VM2000 function should be available for the mirror pubset after the configuration data has been read.
The device attributes PUBRES-FOR-ASSIGNMENT and PUBRES-FOR-ATTRIBUTES are displayed for the pubres device concerned when /SHOW-VM-DEVICE-STATUS is used, see "Assigning and removing pubsets of a VM".
Mirror disks in remote disk storage systems
When the REC function (Remote Equivalent Copy, ETERNUS DX) is used, the data of a local disk storage system is mirrored on remote disk storage systems, see the "SHC-OSD" manual [20].
For such a pubset, the required VM2000 function is executed on all of the pubset’s source units when the *PUBSET-DEVICES operand is specified. The source unit must be specified as the pubres device or registered in the MRS catalog.
Only if VM2000 can access the target units in the remote disk storage system, a target unit can also be specified as the pubres device. The required VM2000 function is then executed on the corresponding target units of the pubset.
The device attributes PUBRES-FOR-ASSIGNMENT and PUBRES-FOR-ATTRIBUTES are displayed for the pubres device concerned when /SHOW-VM-DEVICE-STATUS is used, see "Assigning and removing pubsets of a VM".