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. 

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. 

## 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. 

Note:  To see how IBM Spectrum Protect Snapshot can help your business, see this IBM Knowledge Center web page. 

## 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. 

