Handbook of Local Area Networks, 1998 Edition:LAN Management Click Here! Search the site:   ITLibrary ITKnowledge EXPERT SEARCH Programming Languages Databases Security Web Services Network Services Middleware Components Operating Systems User Interfaces Groupware & Collaboration Content Management Productivity Applications Hardware Fun & Games EarthWeb sites Crossnodes Datamation Developer.com DICE EarthWeb.com EarthWeb Direct ERP Hub Gamelan GoCertify.com HTMLGoodies Intranet Journal IT Knowledge IT Library JavaGoodies JARS JavaScripts.com open source IT RoadCoders Y2K Info Previous Table of Contents Next Archiving Much data is transitory in nature, being active for a short period of time and then dormant for months or even years. Still, data is a valuable commodity and it is impossible to determine when it will be required. Archiving is a technique wherein a particular data set is moved from online primary storage to near-online or offline archival storage media and then deleted from primary storage. This differs from maintaining a file history (backup), which captures copies of files that are still active and online so that they can be retrieved if they are needed. Before data can be considered safely archived and removed from primary storage copies have to be made on multiple media (e.g., three different tapes or two optical platters). Whether archival storage is near-online, offline, or off-site usually depends on the age of the data. Data might be automatically archived to a near-online device after it has been dormant for three months, and then taken offline after six months. Off-site data storage is usually a disaster recovery measure, although sometimes it is convenient simply to save physical space. Archival storage is intended to be long-term storage, so it is important to match the life expectancy of the media to the required data availability. The life span of tape depends on the environment in which it is stored (a computer room environment is recommended) and the care taken with it. Frequent retensioning, or spinning the tape from end to end, will keep it from sticking to itself. With proper care, a ten-year life span is practical. Media vendors make available guidelines on storing tape. Optical disk is a newer technology than tape and is more expensive. Less is known about its durability, however, less environment control is necessary than for tape and a practical life span of 20 to 30 years is probable. An archiving system should provide an easy method for locating archived data. Each tape, optical disk, or other media used for archival storage must be titled and labeled for easy retrieval. This label should be both electronic, as data on the media, and physical, attached to the cartridge, tape, or whatever media is used, in a visible location. The physical label should bear a name, archive data, and general description. The electronic label should duplicate the physical label plus provide information on the contents of the media (e.g., directories and save sets). The same data base that is used for tracking file history for backup should be used for tracking archived files, and the same search techniques should be available. Archived files are most frequently searched for by the file name or by browsing the directory tree of archived data, rather than by the time that they were archived. Whenever data is moved from one device to another, as with archiving, it is crucial to move all directory information (name space) and security (operating system attributes) with it. The removable media used for archiving should be protected by password, physical location, or both. The number of people with physical access to archived media should be kept at a minimum to further protect the privacy of the information contained in the archive. Combining Archiving and Backup Archiving and backup activities are similar and it is convenient to share the file history data base between them. It is important to remember that they serve different purposes and that archived files are intended to be kept for long periods of time while backup files are maintained until they have been superseded and then discarded. Media that are used for archiving are never overwritten, while data integrity tapes are reused on a specific media rotation schedule. The simplest and safest way to combine these two operations is to let them share a media data base, but they should be kept on separate physical media and these media should be treated differently. Backup time and media cost can be reduced by combining the techniques. The modified full backup scheme described earlier reduces the time taken for a full backup by not capturing files that have been copied to three different archival media. As noted earlier, this saves backup time at the expense of restore time. If performing modified full backups is important, it is possible to go one step further and combine backup and archiving on one media. On each weekend backup session the first thing written to a tape is the set of dormant or stable files that have not been captured three times. Then active files are written to tape. The next time this tape is used, any newly dormant or stable files would be appended to the first set of archived files, overwriting the active files. Then active files would be written. This process continues until the tape is full, at which time it is permanently stored offsite. Exhibit 7-4-5 illustrates this combined strategy. Exhibit 7-4-5.  Combining Archive and Backup on One Tape Previous Table of Contents Next Use of this site is subject certain Terms & Conditions. Copyright (c) 1996-1999 EarthWeb, Inc.. All rights reserved. Reproduction in whole or in part in any form or medium without express written permission of EarthWeb is prohibited. Please read our privacy policy for details.