IBM System Storage DS3000, Programming Manual

Page: 468 / 652

When you add a member logical drive to the to the primary Enhanced Global Mirror Group on the local
storage subsystem, the firmware creates a place holder object in the secondary Enhanced Global Mirror
Group on the remote storage subsystem. The placeholder object represents the associated mirror logical
drive. When you add a member logical drive to the secondary Enhanced Global Mirror Group on the
remote storage subsystem, the member logical drive replaces the placeholder object and resolves the
mirror configuration.
After you have created the Enhanced Global Mirrored Pair you will actually have three logical drives in
the relationship:
v
Primary logical drive on the local storage subsystem that holds the original data
v
Secondary logical drive on the remote storage subsystem that holds the duplicate data
v
Repository logical drive on the local storage subsystem that holds the data that was changed on the
primary logical drive
If any member logical drives of the Enhanced Global Mirror Group are actively synchronizing data from
a periodic synchronization interval when the new member logical drive is added, the synchronization
process is halted. Existing recovery points from a past completed synchronization process, if any, are
preserved. After the new Enhanced Global Mirror Group mirror-pair has been initialized, a new
consistent set of recovery points are taken of all member logical drives of the Enhanced Global Mirror
Group.
Guidelines to follow when creating the Enhanced Global Mirror pairs:
v
Primary logical drives and secondary mirror repository logical drives do not need to be the same size.
v
Mirror repository logical drives are independent of the associated primary logical drive and secondary
logical drive so that they can be created in separate arrays with different RAID levels.
v
Mirror repository logical drives must have the same T10PI and Quality of Service (QoS) settings as the
associated logical drives. For example, if a mirrored pair is T10PI enabled, the associated mirror
repository logical drive must be T10PI enabled.
v
Member logical drives on both the local storage subsystem and the remote storage subsystem must be
standard RAID logical drives. They cannot be Enhanced FlashCopy logical drives, views, or repository
logical drives.
Determining if You Have a Secondary Mirror logical drive .
To determine if you have secondary mirror logical drive candidate that is appropriate to your needs on
the remote storage subsystem, run this command on the remote storage subsystem:
show alllogicalDrives summary
This command returns information about the number of logical drives on the storage subsystem, the
names of the logical drives, the capacity, RAID level, and other information. If you run the command
without the summary parameter, you receive several pages of detailed information. However, running
with the summary parameter provides you with enough information to determine which of the logical
drives you might be able to use for a repository logical drive.
Adding a Primary logical drive to the Enhanced Global Mirror Group
Note: You cannot add a primary logical drive to the Enhanced Global Mirror Group if the Enhanced
Global Mirror Group contains orphaned mirror-pair members.
A mirrored relationship between the primary logical drive on the local storage subsystem and the
secondary logical drive on the remote storage subsystem is established by adding a member logical drive
to the Enhanced Global Mirror Group on the local storage subsystem. To add a member logical drive to
the Enhanced Global Mirror Group on the local storage subsystem run this command on the local storage
subsystem:
7-8
IBM System Storage DS3000, DS4000, and DS5000: Command Line Interface and Script Commands Programming Guide