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 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. 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.  11.1.6 Grains and bitmap: I/O indirection IBM Spectrum Protect Snapshot Chapter 11. Advanced Copy Services  465