EMIS - UN-Habitat

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Building an Environmental Management Information System Tool 30: Backing up the EMIS How to ensure the safety of the EMIS data • Why back up data? • What media to use for backups • Backup schedule • Backup software _____________________________________________________________ Why back up data? The EMIS data is valuable. It will cost you time and effort to re-create it, and that costs money; sometimes it isn’t even possible to recreate the data. Since EMIS data is an investment, you should protect it and take steps to avoid losing it. Computers are fast, accurate, and indispensable: however, this is an imperfect world, and things can still go wrong.There are basically four reasons why you might lose data: hardware failures, software bugs, human action, or disasters such as fire. It is recommended that you back up the entire EMIS regularly.When a backup is performed, an exact copy of the system is copied onto a backup medium in compressed format (depending on the backup system). However, like everything else in the physical world, backups will fail sooner or later (physical depletion of the backup media over time). _____________________________________________________________ What media to use for backups The most important decision regarding backups is the choice of backup medium.You need to consider cost, reliability, speed, availability and usability. Several media can be used to back up data: • Hard disks are generally used for backups in networked systems: the data is copied from the workstation’s local hard disk to a file server.You can also install a second hard disk (slave) in your computer and copy your files from the master hard disk to the slave. Size: up to 40 GB • Floppies are the cheapest medium, fairly reliable, very available, but unsuitable for large amounts of data.The software used is the MS Windows internal Backup System. Size: up to 1.4 MB. • Zip-Drives work like floppy drives but use media with more storage space.They can be fairly expensive. The accompanying software usually includes backup schedulers. Size: up to 250 MB. 202
The Toolkit: Key Steps in Building an Environmental Management Information System • Tapes range from cheap to somewhat expensive, are very reliable, and quite available,.Access to individual files is slow. Internal and external tape drives are available. The accompanying software usually includes backup schedulers. Size: up to 3 GB. • CD-ROMs are becoming more popular as backup media. Recordable CD- ROMs are cheap and easily available. Internal and external CD- ROM writers are available.The rate of copying failures is still quite high (approximately 30%, depending on the copied files, network interruptions of hard disc activities during copying). Size: up to 700 MB. _____________________________________________________________ Backup schedule Back up as much as possible.The major exception is software that can be easily reinstalled, but even software may have configuration files that are important to back up, lest you need to do all the work to configure them all over again.The obvious items to back up are user files and system configuration files. A simple backup scheme is to back up everything once, and then to back up everything that has been modified since the previous backup.The first backup is called a full backup, the subsequent ones are incremental backups.A full backup is often more laborious than incremental ones, since there is more data to write to the tape and a full backup might not fit onto one tape (or floppy). Restoration can be optimised so that you always back up everything since the previous full backup: this way, backups take a bit more work, but you should never need to restore more than a full backup and an incremental backup. If you want to make backups every day and have six tapes, you could use tape 1 for the first full backup (say, on a Friday), and tapes 2 to 5 for the incremental backups (Monday throughThursday).Then you make a new full backup on tape 6 (second Friday), and start making incremental ones with tapes 2-5 again. Note: You don’t want to overwrite tape 1 until you’ve got a new full backup, in case a disaster happens while you’re making the new full backup.After you’ve made a full backup on tape 6,you should keep tape 1 somewhere else, so that if your other backup tapes are destroyed in a disaster, you still have at least something left. When you make the next full backup, you use tape 1 and leave tape 6 in its place. For more heavy-duty use, multilevel backups are more appropriate.The method has two backup levels: full and incremental backups.This can be generalised to any number of levels.A full backup would be level 0, and the different levels of incremental backups levels 1, 2, 3... At each incremental backup level you back up everything that has changed since the previous backup at the same or a previous level. The purpose for doing this is that it allows a longer backup history. In the example given in the previous section, the backup history went back to the 203
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Sustainable Cities Programme (SCP)
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The SCP Source Book Series Building
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Introduction and Overview B5.1 Exhi
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List of Acronyms EMF Environmental
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User’s Guide Introduction and Ove
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Part A Introduction and Overview In
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Introduction and Overview with it;
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Introduction and Overview operated
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The SCP project cycle has three mai
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Supporting a new urban management a
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