Business continuity volume ( BCV ) is a symmetrix device with special attributes. It can function either as an additional mirror or a separate host addresable volume. Establishing BCV devices as mirror images of active production volumes allows you to run multiple business continuity tasks in parallel.
Principal device, known as the standard device remains online for regular symmetrix operation from the original production server. Each BCV contains a unique host address, making it accessible to a separate backup/recovery server. When you establish a BCV as a mirror of the standard device, the relationship is known as BCV PAIR. One can imagine a BCV device to be a third component of the mirror.
BCV/standard mirror pairs make it practical for to access the copied data on a BCV at any point in time without interfering in business operations. Any time you split one of the BCV’s from the standard device, BCV has data that is available for backup, testing or analysis.
A Business continuance sequence first involves establishing the BCV device as a mirror of the standard symmetrix device. When a BCV is mirrored with the standard device, the BCV is inaccessible to its host. After the BCV becomes synchronized with its paired standard device, we can split the BCV from the standard device at any time, making the BCV accessible again to its host. After the split, the BCV contains valid data and is available for:
* Business continuance tasks through its original device address
* Restoring data to the standard device if there is a loss of data on the standard device
The device group is the entity that is used to manage and control BCV pairs. Host SYMAPI database file stores information about the device group, the standard and BCVs contained in it. Information about device pairs are stored in the Symmetrix global memory and can be updated by subsequent establisth or restore operations.
When device groups are formed initially, there is a possibility of standard and BCV devices may have a previous pairing relationship with a device that does not belong to the device group. In that scenario, we can use commands to check the association.
1. Discover the symmetrix ; # symcfg discover
2. Get the symmetrix devices ; # symdev list -sid 0123
3. Get the relationship between standard and BCV ; # symbcv list -sid 0123
Setting up Device Groups
A device group can hold any of the three standard devices .
a) Regular ( non-RDF)
b) RDF1 ( source )
c) RDF2 ( target )
Although a BCV cannot be associated with more than one device group at a time, a BCV can be moved from one group to another without the regard for any device group type. However, the movement of standard devices between device groups is possible only if the source and destination groups are of the same type.
The following sequence creates a device group and adds devices to the group:
1. Create a device group named BCVGRP ; # symdg create BCVGRP -type regular
2. Add a standard device ( ex symm device name 080 ) to the device group BCVGRP on the symmetrix number 0123. A default logical name of the form DEV001 is assigned.
# symld -g BCVGRP -sid 0123 add dev 080
3. Associate a BCV ( symm device name 090 ) to the standard device. A default logical name of BCV001 is assigned.
# symbcv -g BCVGRP -sid 0123 associate dev 090
With this we have created a device group of type Regular and have added Standard and BCV devices to the group. We shall now go ahead and create the pairs.
Creating BCV pairs
To assign a BCV as a mirror of a standard symmetrix device, we can use the following steps.
a) Establish a BCV pair explicitly;
# symmir -g BCVGRP -full establish DEV001 bcv ld BCV001
Here we are explicitly pairing DEV001 with BCV001. Use the -full option to copy the contents completly the very first time.
Once a pairing relationship has been created, Symmetrix keep a record of that relationship. One can alter that record only by performing a subsequent establish, restore or cancel operation.