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You will need to establish a regular program of backup for your system. Backups protect you from disk failures as well as human catastrophes such as accidental deletion of data. Here are some general guidelines:
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Most shops back up disk drives to tape. Tapes with sufficient capacity to match today’s disk drives can be expensive; see discussion below.
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A common approach calls for daily backups of all changed data files, and weekly backup of all data on your system. You create “pools” of tapes for your daily and weekly dumps. You might have one tape series for every day of the week (or one each for Monday through Friday) and a separate series for your weekly dumps. The more “depth” to your tape pools, the more confidence you have that you’ve got all your important files are backed up.
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Some sites handle content backup separately from operating system and software backup; some even put software and data on separate disk drives. Because software tends to change at a different pace than content, this can provide important efficiencies. For instance if you make software changes infrequently, you might do a daily “change” dump of your content, and only back up your software weekly. Note that it’s important to capture important configuration files, which tend to reside in the same folders as software; the only sure-fire way to do this is to back up everything.
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It’s very important to periodically store your most critical files off-site. You can do this by taking one of your full dump tape set to an off-site storage location. A safety deposit box at a bank is a good choice. Increasingly network backup is becoming an option; vendors provide ways to archive your most critical files at their site across the Internet.
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If you employ RAID 1 or RAID 5, you may feel confident that your system is adequately backed up. Unfortunately, there have been cases in which RAID systems have failed in such a way that you are not protected. For instance, in some cases, a mirrored drive may fail, and you may not notice the failure. Eventually its mirrored partner fails, and now you have no data and no backup. Bottom line: it’s a good idea to back up all data periodically even when you have RAID protection.
The industry offers data backup drives based on formats created for other purposes. For instance, DAT, or Digital Audio Tape, is a popular format for data backup; it is probably the most commonly-used format for server backup applications. The major formats for server backup are:
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DAT. These drives can hold from 8 gigabytes (8GB) of data up to 24G at a cost from under $1000 for the drive to over $3000, depending on transfer speed and data capacity. Data is backed up onto a 4mm cassette that looks like a DAT tape. Media costs are from $5 per tape to $25 per tape depending on capacity.
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Exabyte, or 8mm. These tapes resemble those used in camcorders. Drives cost $1000 or more. Tapes hold from 2.5 to 7 GB and cost from $5 to $12 each.
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DLT. These half-inch cartridges hold from 10GB to 75GB of data. Drives cost from $2000 to $5000 or more. Tapes cost about $50 each. These are very high-quality, high-performance backup devices.
Note that vendors may quote capacities of “12/24” or similar numbers. The first number is uncompressed; the second number assumes two-to-one compression. If your content is already in a compressed format such as JPEG, or if your backup software does data compression, you won’t achieve an additional two-to-one compression on tape.
In any event, if you buy a drive with sufficient capacity, you may be able to back up your entire Web site onto a single tape. This saves the manual effort of loading “contiunation volumes” during the backup process and can be a great convenience.
In order to perform backups, you will need backup software. Your NT, Unix, or Mac server will come with built-in backup software, but you may find such software to be limited. Commercial backup software tools allow you to schedule backups, manage multiple tape pools, and back up user desktop computers along with your server. In the Windows NT environment, ARCserve from Computer Associates is a popular tool. Seagate Software markets a competing tool, Backup Exec. These tools cost less than $500.
Archiving of content is a concept related to backup. When we speak of archiving, we generally think in terms of taking a snapshot of part or all of our content, with that snapshot kept indefinitely. Archiving can be done to the same tape media you use for backup. Alternatively, you may want to consider CD-R, CD-RW, or the new DVD-RAM as archive formats.
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CD-R allows you to store about 650 megabytes of data on a single CD, which can be read by any PC with a CD-ROM drive. A CD-R probably could not hold an entire CI site including software, but in many cases it could hold most or all of a site’s content. Individual CD-R discs can be found for under $2 each.
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CD-RW offers the advantages of CD-R at a higher media cost – about $12 per disc as of this writing. Unlike CD-R, CD-RW allows a single disc to be written on multiple times. The extra media expense of CD-RW would not be justified for archiving content; by definition, you want to write on an archive disc only once.
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DVD-RAM offers several times the capacity of CD-R – up to 5.2 gigabytes. Thus DVD-RAM could in many cases back up on a single disc an entire CI site, or all of the content of a multimedia-rich site. As of this writing each DVD-RAM blank disc is expensive – $50 or so – but these prices will fall.
These formats can be useful for exchange of data as well. For instance, an off-site content provider may wish to deliver large amounts of content in CD-R form. Your webmaster can retain the CD-R disc or return it to the content provider; either way, another backup copy can be retained.
Other popular archive and exchange formats include Iomega’s ZIP and JAZ drives, and Imation’s Superdisk drives.
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