HP StorageWorks 4000s NAS 4000s and 9000s Administration Guide - Page 94

Shadow Copies Shadow Copy Planning Before setup is initiated on the server and the client interface is made available to end users, consider the following: ■ From what volume will shadow copies be taken? ■ How much disk space should be allocated for shadow copies? ■ Will separate disks be used to store shadow copies? ■ How frequently will shadow copies be made? Identifying the Volume Shadow copies are taken for a complete volume, but not for a specific directory. Shadow copies work best when the server stores user files, such as documents, spreadsheets, presentations, graphics, or database files. Note: Shadow copies should not be used to provide access to previous versions of application or e-mail databases. Shadow copies are designed for volumes that store user data such as home directories and My Documents folders that are redirected by using Group Policy or other shared folders in which users store data. Shadow copies work with compressed or encrypted files and retain whatever permissions were set on the files when the shadow copies were taken. For example, if a user is denied permission to read a file, that user would not be able to restore a previous version of the file, or be able to read the file after it has been restored. Although shadow copies are taken for an entire volume, users must use shared folders to access shadow copies. Administrators on the local server must also specify the \\servername\sharename path to access shadow copies. If administrators or end users want to access a previous version of a file that does not reside in a shared folder, the administrator must first share the folder. Note: Shadow copies are available only on NTFS, not FAT or FAT32 volumes. Files or folders that are recorded by using Shadow Copy appear static, even though the original data is changing. Allocating Disk Space When shadow copies are enabled on a volume, the maximum amount of volume space to be used for the shadow copies can be specified. The default limit is 10 percent of the source volume (the volume being copied). The limit for volumes in which users frequently change files should be increased. Also, note that setting the limit too low causes the oldest shadow copies to be deleted frequently, which defeats the purpose of shadow copies and frustrates users. If the frequency of changes to each file is greater than the amount of space allocated to storing shadow copies, then no shadow copy is created. Therefore, administrators should carefully consider the amount of disk space they want to set aside for shadow copies, and keep in mind 94 NAS 4000s and 9000s Administration Guide