Network backup systems such as Arcserve (Computer Associates), NetBackup (Veritas), Networker (EMC/Legato) and Tivoli Storage Manager (IBM) provide the following services:
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- hierarchical storage management.
The main task of network backup systems is to back data up regularly. To this end, at least one up-to-date copy must be kept of all data, so that it can be restored after a hardware or application error ('file accidentally deleted or destroyed by editing', 'error in the database programming').
The purpose of archiving is to freeze a certain version of the data so that this precise version can be restored later on. For example, after the conclusion of a project its data can be archived on the backup server and then deleted from the local hard disk. This saves local disk space and accelerates backup and restore processes, since only the data that is actually being worked with has to be backed up or restored.
Hierarchical storage management (HSM) finally leads the end user to believe that any desired size of hard disk is present. HSM moves files that have not been accessed for a long time from the local disk to the backup server; only a directory entry remains in the local file server. The entry in the directory contains meta information such as file name, owner, access rights, date of last modification and so on. The metadata takes up hardly any space in the file system compared to the actual file contents, so space is actually gained by moving the file content from the local disk to the backup server.
If a process accesses the content of a file that has been moved in this way, HSM blocks the accessing process, copies the file content back from the backup server to the local file system and only then gives clearance to the accessing process. Apart from the longer access time, this process remains completely hidden to the accessing processes and thus also to end users. Older files can thus be automatically moved to cheaper media (tapes) and, if necessary, fetched back again without the end user having to alter his behaviour.
Strictly speaking, HSM and backup and archive are separate concepts. However, HSM is a component of many network backup products, so the same components (media, software) can be used both for backup, archive and also for HSM. When HSM is used, the backup software used must at least be HSM-capable: it must back up the metadata of the moved files and the moved files themselves, without moving the file contents back to the client. HSM-capable backup software can speed up backup and restore processes because only the meta-information of the moved files has to be backed up and restored, not their file contents.
A network backup system realizes the above-mentioned functions of backup, archive and hierarchical storage management by the co-ordination of backup server and a range of backup clients (Figure 7.1). The server provides central components such as the management of backup media that are required by all backup clients. However, different backup clients are used for different operating systems and applications. These are specialized in the individual operating systems or applications in order to increase the efficiency of data protection or the efficiency of the movement of data.
Figure 7.1 Network backup systems can automatically backup heterogeneous IT environments via the LAN. A platform-specific backup client must be installed on all clients to be backed up.
The use of terminology regarding network backup systems is somewhat sloppy: the main task of network backup systems is the backup of data. Server and client instances of network backup systems are therefore often known as the backup server and backup client, regardless of what tasks they perform or what they are used for. A particular server instance of a network backup system could, for example, be used exclusively for HSM, so that this instance should actually be called a HSM server – nevertheless this instance would generally be called a backup server. A client that provides the backup function usually also supports archive and the restore of backups and archives – nevertheless this client is generally just known as a backup client. In this book we follow the general, untidy conventions, because the phrase 'backup client' reads better than 'backup-archive-HSM and restore client'.
The two following sections discuss details of the backup server (Section 7.3) and the backup client (Section 7.4). We then turn our attention to the performance and the use of network backup systems.
Use the following table of contents to navigate to chapter excerpts or click here to view Network Backup in its entirety.
|ABOUT THE BOOK:|
|Storage networks will become a basic technology like databases or local area networks. According to market research, 70% of external storage devices will be connected via storage networks in 2003. The authors have hands-on experience of network storage hardware and software, they teach customers about concrete network storage products, they understand the concepts behind storage networks, and show customers how storage networks address their business needs. This book explains how to use storage networks to fix malfunctioning business processes, covering the technologies as well as applications -- a hot topic that will become increasingly important in the coming years.Purchase the book from Wiley Publishing|
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|Authors Ulf Troppens and Rainer Erkens are both employed at IBM TotalStorage Interoperability Center in Mainz, Germany a testing, development and demonstration laboratory for storage products and storage networks. Both authors work at the interface between technology and customers. Wolfgang Müller is currently working as a software architect in the Storage Software Development Department at IBM in Mainz, Germany, where the focus is on software development projects supporting open standards such as SMI-S/CIM/WBEM and IEEE 1244.|