If you use tape as a data backup medium, the primary recurring cost is the cost of tapes. Although labor and hardware typically cost more, you should monitor your tape use and replace your tapes according to the manufacturers' recommendations.
The good news about tape costs is that they have generally held steady over the last couple of years. The better news is that there are things you can do to significantly reduce tape use and, in turn, reduce tape cost.
While tape prices did increase in mid-2007, over the last few years, they have been generally stable. In 2003, a Super DLT 1 tape cost approximately $50. In May 2008, the price for the same tape was $45. Currently, the short-term trend in tape prices is mostly decreasing. This reflects the 2007 spike and the slowing economy in late 2007 and 2008.
Tape costs are simply another argument for pruning data before putting it on tape. At the simplest level, you need to decide what you should be backing up. A lot of stuff, like .tmp files and browser caches, don't need to be backed up at all. With the use of snapshot features like Windows System Restore and inexpensive third-party imaging applications like Acronis True Image, files and folders can be recovered from disk in the event of an accident or error. That being the case, only the things you really need to save should be put on tape.
Backup software gives you the option of deciding which partitions, files and folders to back up. By choosing wisely you can greatly reduce the amount of data that goes on tape. Organization can help here. If you concentrate the files you need to back up into one or more partitions, you can back them up more easily. One common strategy is to set up one or more data partitions that hold just the data from your a...
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pplications. The applications themselves are kept elsewhere and either not backed up, (on the theory you can reinstall them if needed) or backed up very infrequently.
Compression is another way to save tape. Most tape systems can compress data an average of 2 to 1, so it only takes half as much space on tape. However, this is highly dependent on the redundancy in the data being backed up, so you need to check to see how much compression you're actually getting. If you're not compressing your data on tape, you should seriously consider doing so.
Another method is to use differential or incremental backups, which only back up files or blocks which have changed. Differential backup backs up everything that has changed since the last full backup, while incremental backup only backs up changes made since the last backup of any kind. Both methods trade tape use for restore time. Incremental backup takes the longest to restore since you have to get data off of all the tape sets to do a complete restore.
Data deduplication is a more sophisticated strategy for shaving tape costs. This relies on software (or sometimes hardware) to comb through your data and eliminate duplicate files or blocks. The duplicates are replaced by pointers to one copy of the data and the files are automatically expanded on restore. On some kinds of files, notably email, deduplication can reduce the amount of data written to tape by 50% or more.
One economy measure you do not want to try is using tapes longer than the manufacturer's recommendation. Tapes have a definite lifespan, typically measured in passes over the head (which manufacturers often express as the times the tape should be used). While the tape maker's figures are conservative, it is better not to exceed them. After all, you want to make sure you can get that data back if you need it.
About the author: Rick Cook specializes in writing about issues related to storage and storage management.
