Date: Mon, 11 Oct 1999 22:48:48 +0200 (CEST) From: Marc Veldman <freebsd@planet.nl> To: Arcady Genkin <a.genkin@utoronto.ca> Cc: freebsd-questions@FreeBSD.ORG Subject: Re: Why use tape for backups? (was: backup method reccommendation?) Message-ID: <Pine.BSF.4.10.9910112034130.1603-100000@lurkie.wxs.nl> In-Reply-To: <87iu4etzlp.fsf_-_@main.wgaf.net>
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Hello Arcady, > It seems to me that it's much cheaper, faster, and more reliable to > just buy another hard drive and dedicate it for backups. The short reactions to what you say are: No, no, and no. The way you do backups depends on how much you value your data, and how fast you want your data to be available after a failure. (Failure meaning hardware errors, software bugs and human errors , as well as various disasters that do not have a direct relation to your computer system like war, theft or natural disasters.) Choosing a backup system and backup procedure is a matter of how fast, and how much, you want your data to be available. You can image that in a very critical system like an AWACS plane in combat or a nuclear power plant or an airline reservation system, you would want your most recent data available as soon as possible. In most professional environments, people hedge their bets: 1.They build a second, completely seperate, out-of-the way computer system to replace/mirror the first. A very expensive option. Nevertheless essential for banks, stock exchanges, military systems etc... 2.They use a RAID(5) system for single harddisk failures. Very common. 3.They make backups to restore accidentally removed files. (human error is the most common reason for restore operations) An often underestimated and overlooked problem. No RAID protects against 'rm -rf /' ..........) 4.They keep enough backup media to be able to recover from (usually human) failures discovered after a period of time longer than one backup cycle. 5.They move their backups offsite to be able to deal with big failures like fire, theft, riots, tornadoes, whatever. If you make your 'backups' to a single harddisk inside your computer, you basically protect yourself against single harddisk failure and early discovered accidental removal of files. If you can live with that, fine. If not, think about a better backup system. Backups are a form of disaster recovery, and more a matter of following sensible(!) procedures than of spending money. In a commercial system, only making daily backups to another harddisk is, in my view, never an option. If your critical data fits on a floppy disk, it can make more sense to make a daily copy to a floppy disk than to buy a DLT tape robot. You keep all floppy disks for a month, and then you put them in a shoebox, and give them your brother who lives a 100 km./miles away. Backups are a form of insurance. If you want better coverage, you pay more. (Or you expend more effort.) > Is there any reasons tapes are a better choice? In a home/personal environment, you might very well get away with your installation CDROMs and a few floppy disks with copies of local your local configuration files in /etc, /usr/local/etc and the like. In a commercial environment, there are a lot of reasons: If you want to archive files, there is simply no way around removable media. Harddisk are too expensive. At this moment, tapes (including collections of tapes like the tape magazines in an HP 1553 autoloader) can contain more data than all single harddisks. If your critical data fills a RAID-array, nothing but a tape magazine will take the amount of data (And will be as easily replacable. In my company we run a Sun E450 with 10x4 GB harddisks...) Note: If you want to take your backups off-site, nothing but removable media is an option. You cannot remove a harddisk without shutting down the whole system. In backup procedures, it is imperative that backups can run without human intervention. Backup procedures that need human intervention are very vunerable, especially in small/medium business environments. (Will you change the harddisk for a weekly backup at Friday 21:00 ? Every Friday ? Really ? You still with me ? Now will you shut down the system and remove the harddisks and restart your system ??) With tapes and with CD-ROMs and floppy disks etc., the medium is seperated from the drive. This makes tapes and CD-ROMs cheaper than harddisks and, more importantly, easier to seperate from the drive. You can easily store an arbitrary amount of media and a few tape/CD/DVD drives at a remote location. A 12 GB tape is still cheaper (and a lot smaller, and more shock resistant) than a 12 GB Harddisk. In short: If you use your system in a personal environment, your mileage may vary. At home, I make backups of my most important config files every day (all right most.., all right usally, .......) Getting a -stable system back on track usually takes eight hours for me. I have the habit of frequently wiping one of my personal systems to practice restores. With the backups of the config files it is a pain. Without the backups it is a major pain. In a commercial environment, there is no way around removable media. The best and cheapest removable media are tapes. Preferrably enough media to allow restores of at least a month old, and with some fairly recent media a good way offsite. Sorry for the long reply. I still have some bruises from some bad crashes. =========================================================================== Get off the keyboard you furry feline ! Marc Veldman, CFBSDN (Certified FreeBSD Newbie) To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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