Flashcopy: How It Works - IBM DS3000 Introduction And Implementation Manual

Draft Document for Review August 30, 2007 12:59 am

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
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.
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.
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
logical drive
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
Base logical drive.
Typically, you create a FlashCopy so that an application (for
where it stores FlashCopy metadata and copy-on-write data (Figure 8-55). It will
Base Logical
Volume
A
Change to W
C
Change to X
E
F
G
Change to Y
Change to Z
J
K
L
Repository Logical
Volume
Metadata
pointer Map
}
B
D
Copy-on-Write
Data
H
I
Read
Write
Chapter 8. Administration - Configure
7065Admin_Configure.fm
FlashCopy repository
Data
Original
Overwritten
Free
I/O Behaviour
Base FlashCopy
Check Map:
Read from
Direct Read
Repository if
from Base Drive
data were
changed
Check Map: Check Map:
Copy Original to Overwrite or
Repository and establish new
overwrite Base mapping
171