Backup and Restore Technologies for Windows
- Reasons for Backup and Restore
- Backup Problems
- Backup Classifications
- Windows 2000 Backup Utility
- Techniques to Create a Volume Snapshot
- Windows XP and Windows Server 2003 Volume Shadow Copy Service
- Windows-Powered NAS Devices and Snapshots
- Network Data Management Protocol
- Practical Implications
Backup is the process whereby a coherent copy of data is made. Backup has become more important as the amount of data has exploded, not just in importance, but in volume as well. One study estimates that more data will be created in the next few years than has been created since the dawn of history! It is interesting to compare the growth in data storage with the more widely known and appreciated growth in electronic chip density. Recall that Moore's law implies that the amount of electronics on a given chip area doubles every 18 months. A lot of industry analysts believe that the growth in digital storage is actually handily beating Moore's law in the sense that the amount of data doubles in much less than 18 months.
Historically, tape has been used as a medium for backing up data. Initially tape was a much cheaper medium than disk. Subsequently it was argued that optical media would become the media of choice, but for various reasons this vision never came to fruition. Although the medium of choice (for backup) remains predominantly tape, regular disk drives are increasingly becoming the medium of choice for an initial backup and system mirror. This trend is due mainly to the falling prices of disk storage, which reduces the cost advantage of tape over disk storage. Another reason for the increasing use of disk-based backup is the higher speed, which ensures minimal downtime for server-based applications.
Note that both disk and tape as media for backup have their advantages and disadvantages, and both will continue to be used. Tape-based backup/restore offers a very high-density medium that can easily be transported for off-site archive or disaster recovery purposes. When an initial copy of data is made to disk, very often a secondary backup operation to traditional tape media is made from that disk-based copy.
This chapter explains the technical challenges that need to be solved in order to back up and restore data in a timely way. The chapter also explains the various ways in which backup/restore techniques can be classified. Also included are discussions of new developments in Windows Server 2003 for accomplishing snapshots (volume shadow copy service) and of the Network Data Management Protocol (NDMP) and how it fits into the Microsoft vision of storage management.
5.1 Reasons for Backup and Restore
Backup is performed for various reasons, and those reasons very often dictate the investment made in accomplishing the backup. The assurance of data availability is the primary reason for creating backups. The higher the data availability requirements, the more investment needs to be made. For example, one form of backup that runs continuously is disk mirroring, in which every data write operation is reflected to another disk to guarantee extremely high data availability.
Data archival also is used to meet legal and other needs in which the data does not have to be accessible immediately but can be produced on demand in a reasonable amount of time, measured in hours, days, or weeks.
Backups are sometimes used to transport datafor example, when one decides to create another data center at a distant geographical location. A similar motivation is to migrate the data to new hardware or, more rarely, a different server platform.