A platform-specific client (backup agent) is necessary for each platform to be backed up. The base client can back up and archive files and restores them if required. The term platform is used here to mean the various operating systems and the file systems that they support. Furthermore, some base clients offer HSM for selected file systems.
The backup of file systems takes place at file level as standard. This means that each changed file is completely retransferred to the server and entered there in the metadata database. By using backup at volume level and at block level it is possible to change the granularity of the objects to be backed up.
When backup is performed at volume level, a whole volume is backed up as an individual object on the backup server. We can visualize this as the output of the Unix command 'dd' being sent to the backup server. Although this has the disadvantage that free areas, on which no data at all has been saved, are also backed up, only very few metadata database operations are necessary on the backup server and on the client side it is not necessary to spend a long time comparing which files have changed since the last backup. As a result, backup and restore operations can sometimes be performed more quickly at volume level than they can at file level. This is particularly true when restoring large file systems with a large number of small files.
Backup on block level optimizes backup for members of the external sales force, who only connect up to the company network now and then by means of a laptop via a dial-up line. In this situation the performance bottleneck is the low transmission capacity of modem or ISDN connections. If only one bit of a large file is changed, the whole file must once again be forced down the dial-up connection. When backing up on block level the backup client additionally keeps a local copy of every file backed up. If a file has changed, it can establish which parts of the file have changed. The backup client sends only the changed data fragments (blocks) to the backup server. This can then reconstruct the complete file. As is the case for backup on file level, each file backed up is entered in the metadata database. Thus, when backing up on block level the quantity of data to be transmitted is reduced at the cost of storage space on the local hard disk.
In addition to the standard client for file systems, most network backup systems provide special clients for various applications. For example, there are special clients for MS Exchange or Lotus Domino that make it possible to back up and restore individual documents. We will discuss the backup of file systems and NAS servers (Section 7.9) and databases (Section 7.10) in more detail later on.
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|
|ABOUT THE AUTHOR:|
|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.|