Chapter 8. Administration - Configure
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Draft Document for Review August 30, 2007 12:59 am
7065Admin_Configure.fm
8.4.1 FlashCopy: How it works
In the DS3000 Storage Manager, the logical drive which will be the source of the FlashCopy is
called the
Base logical drive.
Typically, you create a FlashCopy so that an application (for
example, a backup application) can access the FlashCopy and read the data while the base
logical drive remains online to users and applications. The FlashCopy drive in this case, is
temporary - it is usually disabled rather than deleted when the backup completes.
You can also create multiple FlashCopies of a base logical drive and use the copies in write
mode to perform 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 provided by the Storage Management software to
help decide how to configure the live database system.
When you initiate a FlashCopy, the controller suspends I/O to the base logical drive for only a
few seconds. Meanwhile, it creates a new logical drive called the
FlashCopy repository
logical drive
where it stores FlashCopy metadata and copy-on-write data (Figure 8-55). It will
build a metadata database which contains only pointers. When the controller finishes creating
the FlashCopy repository logical drive, I/O write requests to the base logical drive can
resume.
Figure 8-55 Flash Copy Read and write schema
Tip: For analysis, data mining, and testing without any degradation of the production
logical drive performance, you can use FlashCopy together with VolumeCopy, as explained
in 8.5.1, “Introduction to VolumeCopy” on page 184.
A
Change to W
C
Change to X
E
F
G
Change to Y
Change to Z
J
K
L
Original
Overwritten
Free
Direct Read
from Base Drive
Check Map:
Read from
Repository if
data were
changed
Check Map:
Copy Original to
Repository and
overwrite Base
Check Map:
Overwrite or
establish new
mapping
Read
Write
Base
FlashCopy
I/O Behaviour
Base Logical
Volume
Data
}
Metadata
pointer Map
Repository Logical
Volume
B
D
H
I
Copy-on-Write
Data
