Introduction to FlashCopy Logical Drives


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Risk of application errors – You cannot create a flashcopy for a that contains unreadable sectors.

A flashcopy logical drive is a point-in-time image of a logical drive. A flashcopy logical drive is the logical equivalent of a complete physical copy, but you create a flashcopy logical drive much more quickly than a physical copy, and the flashcopy logical drive requires less disk space. The logical drive from which you are basing the flashcopy, called the , must be a in your . Typically, you create a flashcopy so that a software application, such as a backup application, can access the flashcopy and read the data while the base logical drive stays online and is user accessible. When the backup completes, the flashcopy logical drive is no longer needed.

You also can create several flashcopys of a base logical drive and write data to the flashcopy logical drives for testing and analysis. Before you upgrade your database management system, for example, you can use flashcopy logical drives to test different configurations. Then you can use the performance data that is provided by the storage management software to help you decide how to configure your live database system.

When you take a flashcopy, the suspends I/O to the base logical drive for a few seconds. During this time, the controller creates a physical logical drive, called the , to store flashcopy metadata and data. When the controller is finished creating the flashcopy repository logical drive, I/O write requests to the base logical drive can continue. However, before a data block on the base logical drive is modified, a copy-on-write occurs. The copy-on-write operation copies the contents of blocks that are to be modified into the flashcopy repository logical drive for safekeeping. Because the flashcopy repository logical drive stores copies of the original data in those data blocks, further changes to those data blocks write directly to the base logical drive without another copy-on-write. The only data blocks that are physically stored in the flashcopy repository logical drive are those that have changed since the time of the flashcopy. Therefore, the flashcopy technology uses less disk space than a full physical copy.

When you create a flashcopy logical drive, you specify where to create the flashcopy repository logical drive, its capacity, and other parameters. You can disable the flashcopy when you are finished with it, such as after a backup completes. Then, you can re-create the flashcopy the next time you perform a backup and reuse the same flashcopy repository logical drive. Because you do not need to create a new flashcopy repository logical drive, you can select Disable FlashCopy >> Re-create FlashCopys to provide a shortcut to create a new flashcopy logical drive of a particular base logical drive. You also can delete a flashcopy logical drive, which also deletes the associated flashcopy repository logical drive.

The storage management software shows a warning message when your flashcopy repository logical drive nears a user-specified threshold, which is a percentage of its full capacity. The default value is 50 percent. When this condition occurs, you can use the storage management software to expand the capacity of your flashcopy repository logical drive from free capacity on the . If you are out of free capacity on the array, you can add unconfigured capacity to the array to expand the capacity of the flashcopy repository logical drive.

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