Installation and User's Guide - Services and Support

IBM Confidentiallonger needed, the local backup manager must free the Target Volume LUNs to thestorage subsystem so that these LUNs can be used for future backup operations.Tivoli Storage Manager automatically detects these situations and performs thereconciliation.ImportantTivoli Storage Manager requires that sufficient storage space be available to createshadow volumes required for VSS Backup processing. Even when the VSS Backupdestination is the Tivoli Storage Manager server, storage space to create a shadowvolume is still required (though on a temporary basis). Since the value of theverexists parameter (specified for your local backup policy) determines the numberof backup versions to retain on local shadow volumes, a verexists=1 setting willcause the deletion of an existing backup on local shadow volumes (during a VSSBackup to Tivoli Storage Manager server storage) in order to create enoughtemporary space for the new snapshot. Therefore, if you want to keep N backupson local shadow volumes and also perform VSS Backups to Tivoli Storage Managerserver storage, make sure you provision enough storage space on local shadowvolumes and specify verexists=N+1.Make sure to specify a verexists value that accommodates your VSS Backup goals.If you have limited storage space for VSS operations and are restricted to averexists=1 setting, you can take advantage of the Backup Destination BOTHoption. This stores the backup on local shadow volumes as well as sends a copy toTivoli Storage Manager server storage.It is possible for VSS Backups (that Data Protection for Exchange creates and storeson local shadow volumes) to be modified and deleted from outside of TivoliStorage Manager control. For example, the Microsoft VSSADMIN DELETESHADOWS command can remove a VSS Backup managed by Tivoli StorageManager without Tivoli Storage Manager being able to prevent such a removal. Insuch a situation, Tivoli Storage Manager recognizes the backup removal andreconciles its index of available backups with what resides on local shadowvolumes. It is important to be aware of this potential for removal and establish astrategy that protects VSS Backup data stored on local shadow volumes from beingcompromised.Be aware that the following issues impact your Tivoli Storage Manager policy formanaging VSS Backups:v Overall backup strategy.v Length of time that VSS Backups will reside on Tivoli Storage Manager serverstorage.v Number of VSS Backup versions to reside on Tivoli Storage Manager serverstorage.v Types of VSS Backups to reside on Tivoli Storage Manager server storage.v Number of VSS Backup versions to reside on local shadow volumes.v Types of VSS Backups to reside on local shadow volumes.v The amount of available target volume storage provisioned for VSS operations.Chapter 1. Data Protection for Exchange Overview 19