IBM System storage DS6000 Series, Введение и руководство по планированию, Страница: 27 / 119

The fast reverse option allows you to reverse a FlashCopy relationship without
waiting for the background copy of a previous FlashCopy to finish.
In disaster recovery situations, when you use Global Mirror, you must use volumes
with consistent data at the target site. Part of the setup requires that you enable the
fast restore option, a copy option that is available for FlashCopy operations. (This
option applies to a Global Mirror operation, which is based on existing Global Copy
and FlashCopy operations at the target site.)
Use fast restore option to reverse a FlashCopy target volume and allow consistent
data to be copied back to its associated source volume, without having to wait for
the background copy from the original source to the original target to complete. You
can then vary the volumes online and start your applications.
You can enable the fast reverse option by accessing Copy Services functions from
the Web interface called the IBM TotalStorage DS Storage Manager and navigating
to the FlashCopy page and then to the Select copy options page.
Global Mirror consistency groups:
Global Mirror can control the formation of consistency groups for data consistency.
Global Mirror is based on a combination of Global Copy and FlashCopy functions.
To support consistent data across storage units, Global Mirror uses a function called
sessions for forming consistent copies. A consistency group is a collection of
volumes across multiple storage units that are managed together when creating
consistent copies of data. The formation of these consistency groups is coordinated
by the master storage unit, which sends commands over remote mirror and copy
links to its subordinate storage units.
With Global Mirror functions, consistency groups can be formed many times per
hour, as opposed to once or twice per day. By combining many volumes into a
session, which is managed by the Global Mirror master storage unit, multiple
volumes can be copied to the recovery site simultaneously while maintaining
point-in-time consistency across those volumes.
The following properties control how often consistency groups are formed. You can
modify these values using the Web-based interface called the IBM TotalStorage DS
Storage Manager. Access the Global Mirror page, and then Define Properties from
the summary of actions menu.
Consistency group interval time
Indicates how long (in seconds) that the storage unit waits between the
formation of consistency groups. If you set this value to zero (requires
sufficient bandwidth), the consistency group forms continuously, which
means that a consistency group starts forming as soon as the previous
consistency group has been formed.
Maximum coordination interval
Indicates the maximum time (in milliseconds) that the master storage unit
communicates with its subordinate storage units to form a consistent data
point. The default is 50 milliseconds.
Because host write I/O is delayed while the consistent point is being set,
performance might be affected by allowing too much time for this interval. If
the time set for the maximum coordination interval expires before formation
of the consistent data point is complete, the consistency group fails.
Chapter 1. Introduction
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