Fault tolerance isn't fault invulnerability. No matter how hard we work to avoid single points of failure, sooner or later something catastrophic will happen to a part of our network. Don't get me wrong, I'm no pessimist - quite the opposite! But part of being a world-class network manager is having a disaster recovery plan in place, and in place before disaster strikes. It doesn't do you any good to implement a data backup strategy after data is lost!
I bring that point up because having a sound backup system in place is a vital part of administering a network. If an email server in your network right now, would you have a backup to restore as much data as possible? Take it from me -- you better.
It's rare to find a network that has no backup system in place, but whether that system is current is often another matter. Personally, I've visited networks where they had a tape drive right there in the server room, with tapes right next to it, and no system in place. Everyone thought someone else was supposed to be handling it (or hoped someone else was), the tapes had no dates, etc. That's exactly where you and I do not want to be.
Part of developing a data backup strategy is deciding how often to run backups, and what kind of backups to run. It's not always feasible to back up all data on every single server every single night. Let's look at the different backup types and exactly what gets backed up when they're run.
Files have an archive bit that indicates whether the file has been changed since the last backup ran. When a file is backed up, this bit is set to "off". When a new file is created or an old file's contents are altered, this bit is set to "on". Keep this archive bit in mind during the following discussion.
A full backup is just what it sounds like. All files are backed up, regardless of the archive bit setting. That's the easy one. Watch these next two. :) The difference is subtle, but significant.
An incremental backup backs up all files created or changed since the last backup of any kind. Every single file with the archive bit set to "on" is backed up.
A differential backup backs up everything that is different -- that is, all files created or changed -- since the last full backup only.
Now you may be thinking, "What in the heck do we need both of those for? What's the real difference?" Believe it or not, this wasn't developed just to make your Network+ exam harder. It just seems that way!
Your choice of backups depends largely on the amount of time you have to run your backups and how much data will have to be stored. Many network administrators choose to run full backups only on weekends and either incremental or differential backups during the week.
One network I was the admin for had this backup schedule:
Every Sunday - full
Every Tuesday - incremental
Every Thursday - incremental
I was lucky enough to never have to use the backups, but let's say that on Saturday morning, a drive went bad. Since I used incremental backups, I needed the last full backup and both of the incremental backups. If I had run differential backups, I would have needed only the last full backup and the last differential backup.
The type of backups your network will run really depends on three factors:
the amount of data to be backed up
the capacity of the backup media
the time available for the backup
If you can run full backups every night, great; if you can't, differential backups are a great middle ground between full and incremental backups. The important thing is that you do run them!
Chris Bryant, CCIE #12933, is the owner of The Bryant Advantage, home of over 100 free CCNA exam and Network + tutorials, The Ultimate CCNA Study Package, Ultimate Network+ Study Package, and Ultimate CCNP Study Packages. You can also join his RSS feed and visit his blog, which is updated several times daily with new Cisco certification articles, free tutorials, and twice-daily CCNA, Network+, and CCNP certification exam practice questions! Details are on the website. For a FREE copy of his latest e-books, "How To Pass The CCNA" and "How To Pass The CCNP", visit the website and download your free copies. You can also get FREE CCNA and CCNP exam questions every day! And now, you can earn your Security + certification from The Bryant Advantage! |