IBM System Storage DS3000, Programming Manual

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The following properties are shared between the local storage subsystem and remote storage subsystem:
v
World Wide Name
v
User label
v
Mirrored I/O Channel Type: Fibre Channel or iSCSI
v
Resynchronization interval
v
Alert threshold for resynchronization completion time (for example, alert if the resynchronization takes
too long)
v Alert threshold for recovery point degradation (such as, age of the Secondary PiTs)
v
Repository utilization warning threshold
The shared properties are communicated to the remote storage subsystem when you create the Enhanced
Global Mirror Group. Changes to a shared property are made first on the local storage subsystem then
communicated to the remote storage subsystem. If a shared property fails change on both the local
storage subsystem and the remote storage subsystem, the local storage subsystem is considered to be the
master setting. When the two storage subsystems reconnect after a communication outage or reboot, the
Enhanced Global Mirror Group properties are reconciled from the local storage subsystem.
If the two storage subsystems detect a dual role conflict after a communication outage is resolved, the
Enhanced Global Mirror Group properties are not reconciled until the dual-role conflict is resolved. To
resolve the role conflict you must determine which storage subsystem is the primary storage subsystem.
At that time, the Enhanced Global Mirror Group properties are then assumed from the side that you have
defined to be the primary side.
Mirror repository logical drives
A mirror repository logical drive is a special logical drive in the storage subsystem that is created as a
resource for the controller owner of the primary logical drive in a remote mirrored pair. The controller
stores mirror information on this logical drive, including information about remote writes that are not yet
complete. The controller can use this information to recover from controller resets and the accidental
powering down of the storage subsystems.
Mirror repository logical drives are used to manage mirror data synchronization. Mirror repository logical
drives are required for both the primary and secondary logical drives in a mirror pair. This mirror
repository logical drive management is different from the Enhanced Remote Mirroring premium feature
where a single mirror repository is set up once and then used for all Enhanced Remote Mirroring
relationships.
The mirror repository pair stores three types of data:
v
Copy-on-write repository data that is used for preserving resynchronization images on the
mirror-primary and recovery point images on the mirror-secondary. The copy-on-write repository is
structurally similar to the repository use for Enhanced FlashCopy groups.
v
A pair of delta logs that are used to track regions of the mirror-primary logical drive that are written
between synchronization intervals. Even though the delta logs are only used on the primary side of the
mirror, they are also allocated on the secondary side to support a role-reversal.
v
A log that tracks synchronization statistics on each mirror pair.
Enhanced Global Mirroring repository logical drives are expandable repository logical drives (ERV). The
minimum mirror repository size is the greater of either:
v
0.02 percent of the base logical drive capacity (regardless of role)
v
32 MB
You can expand the capacity of the mirror repository logical drives using the standard rules for ERV
expansion. You cannot reduce the size of the mirror repository logical drives.
7-4
IBM System Storage DS3000, DS4000, and DS5000: Command Line Interface and Script Commands Programming Guide