IBM System Storage DS3000, Programming Manual

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Note: When you first create a FlashCopy repository logical drive, briefly stop all of the write operations
to the base logical drive so that a stable image of the base logical drive is available.
When the host writes to the base logical drive, the new data is also copied to the FlashCopy repository
logical drive. This action is called
copy-on-write . A FlashCopy is constructed by combining the updated
data in the FlashCopy repository logical drive with data in the base logical drive that has not been
altered. This action creates a complete copy of the base logical drive at a specific point in time. The
FlashCopy appears as a logical drive that contains the original data at the time of creation, but the
FlashCopy is actually an image that is the combination of the FlashCopy repository logical drive and the
original base logical drive. The FlashCopy repository logical drive, which houses original data that has
been changed, is the only additional disk drive space that is needed for the FlashCopy logical drive. The
additional disk drive space is typically 10 percent to 20 percent of the disk drive space of the base logical
drive and varies depending on the amount of changes to the data. The longer a FlashCopy logical drive
is active, the larger the FlashCopy repository logical drive must be. The default size of the FlashCopy
repository logical drive is 20 percent of the base logical drive; however, you can set the size of the
FlashCopy repository logical drive to other values.
You can read, write, and copy a FlashCopy logical drive. Data written by a host to the FlashCopy logical
drive is handled in the FlashCopy repository logical drive. When a write occurs to the base logical drive
of a FlashCopy logical drive, the new data also overwrites the appropriate FlashCopy repository logical
drive data. The following table lists the FlashCopy logical drive commands.
Table 5-2. FlashCopy Logical Drive Commands
Command Description
create flashcopyLogicalDrive
This command creates a FlashCopy logical
drive.
re-create flashcopy
This command starts a fresh copy-on-write
operation by using an existing FlashCopy
logical drive.
re-create flashcopy
collection This command restarts multiple FlashCopy
logical drives as one batch operation using one
or many existing FlashCopy logical drives.
set (flashcopyLogicalDrive) This command defines the properties for a
FlashCopy logical drive and lets you rename a
FlashCopy logical drive.
stop flashcopy
This command stops a copy-on-write
operation.
Creating a FlashCopy Logical Drive
The
create FlashCopyLogicalDrive
command provides three methods for defining the disk drives for
your FlashCopy repository logical drive:
v
Defining the disk drives for the FlashCopy repository logical drive by their enclosure IDs and their slot
IDs
v
Defining an subsystem in which the FlashCopy repository logical drive resides. In addition, you can
define the capacity of the FlashCopy repository logical drive.
v
Defining the number of disk drives, but not specific disk drives, for the FlashCopy repository logical
drive.
When you use the
create FlashCopyLogicalDrive
command to create a FlashCopy logical drive, the
minimum information that you need to provide is the standard logical drive that you want to use for the
5-2
IBM System Storage DS3000, DS4000, and DS5000: Command Line Interface and Script Commands Programming Guide