NetBackup™ Snapshot Client Administrator's Guide
- Introduction
- Installation
- Policy configuration
- Selecting the snapshot method
- About using alternate client backup
- Configuring alternate client backup
- Policy configuration tips
- About disabling snapshots
- NAS snapshot configuration
- Dynamic data streaming for D-NAS workloads
- Setting up a NAS-Data-Protection policy
- FlashBackup configuration
- Instant Recovery configuration
- About Instant Recovery
- About sizing the cache for Instant Recovery copy-on-write snapshots
- About storage lifecycle policies for snapshots
- Configuration of software-based snapshot methods
- Support for Cluster Volume Manager Environments (CVM)
- Configuration of snapshot methods for disk arrays
- OS-specific configuration tasks
- About IBM DS6000 and DS8000 arrays
- Configuring NetBackup to access the IBM DS6000 or DS8000 array
- About IBM DS4000 array
- About Hitachi SMS/WMS/AMS, USP/NSC, USP-V/VM
- Hitachi array software requirements
- About HP-XP arrays
- About array troubleshooting
- Notes on Media Server and Third-Party Copy methods
- Backup and restore procedures
- Snapshot management
- Troubleshooting
- Logging directories for UNIX platforms
- Logging folders for Windows platforms
- FlashBackup and status code 13
- Appendix A. Managing nbu_snap (Solaris)
- Appendix B. Overview of snapshot operations
About quiescing the system
Before a useful snapshot can be created, the data to back up must be transactionally consistent or complete. A transaction is a single data action, such as updating a patient's record in a medical database, or creating a record for a new patient. Such a transaction is composed of multiple I/O requests (search, copy, send, write, and so forth). Until the transaction's I/O requests are complete, the data is inconsistent and may be unsuitable for backup.
Transactions affect all levels of the storage management stack (file system, volume manager, and so forth). A transaction generates further transactions as a request is handed off to the next level of the stack. For instance, in the file system, an I/O request from a database application constitutes a transaction and may be split into many disk references. All these disk references must be complete for the original request to be fulfilled. Thus, the creation of the snapshot must be coordinated with any application or process that can affect the transactional consistency of the data.
The means of coordination is called quiesce (literally, to make quiet or place in repose). Quiesce involves pausing the database application or process until the data is transactionally consistent. Applications and the storage management stack must all be quiesced before a useful snapshot can be made.