Chapter 11. Advanced Copy Services 441
Various operating systems and applications provide facilities to stop I/O operations and 
ensure that all data is flushed from host cache. If these facilities are available, they can be 
used to prepare for a FlashCopy operation. When this type of facility is unavailable, the host 
cache must be flushed manually by quiescing the application and unmounting the file system 
or drives.
The target volumes are overwritten with a complete image of the source volumes. Before the 
FlashCopy mappings are started, any data that is held on the host operating system (or 
application) caches for the target volumes must be discarded. The easiest way to ensure that 
no data is held in these caches is to unmount the target volumes before the FlashCopy 
operation starts.
IBM Spectrum Protect Snapshot
IBM FlashCopy is not application-aware and a third-party tool is needed to link the application 
to the FlashCopy operations.
IBM Spectrum Protect Snapshot protects data with integrated, application-aware snapshot 
backup and restore capabilities that use FlashCopy technologies in the IBM Spectrum 
Virtualize.
You can protect data that is stored by IBM Db2® SAP, Oracle, Microsoft Exchange, and 
Microsoft SQL Server applications. You can create and manage volume-level snapshots for 
file systems and custom applications.
In addition, it enables you to manage frequent, near-instant, nondisruptive, application-aware 
backups and restores that use integrated application and VMware snapshot technologies. 
IBM Spectrum Protect Snapshot can be widely used in both IBM and non-IBM storage 
systems.
11.1.6  Grains and bitmap - I/O indirection
When a FlashCopy operation starts, a checkpoint is made of the source volume. No data is 
copied at the time that a start operation occurs. Instead, the checkpoint creates a bitmap that 
indicates that no part of the source volume was copied. Each bit in the bitmap represents one 
region of the source volume. Each region is called a grain.
You can think of the bitmap as a simple table of ones or zeros. The table tracks the difference 
between a source volume grains and a target volume grains. At the creation of the FlashCopy 
mapping, the table is filled with zeros, which indicates that no grain is copied yet. When a 
grain is copied from source to target, the region of the bitmap referring to that grain is updated 
(for example, from “0” to “1”), as shown in Figure 11-2 on page 442.
Preferred practice: From a practical standpoint, when you have an application that is 
backed by a database and you want to make a FlashCopy of that application’s data, it is 
sufficient in most cases to use the write-suspend method that is available in most modern 
databases. This is possible because the database maintains strict control over I/O. 
This method is as opposed to flushing data from both the application and the backing 
database, which is always the suggested method because it is safer. However, this method 
can be used when facilities do not exist or your environment includes time sensitivity.
Note: For more information about how IBM Spectrum Protect Snapshot can help your 
business, see this IBM Knowledge Center web page.