Why Are Server Backups So Painful?

{excerpt}Why backups have such a dramatic impact on server performance. {excerpt}

Data sets are growing rapidly, and storage is always the most precious commodity a server has. Above is a graph of hard disk capacity availability as it has grown over the years. These numbers are compiled using data from [http://www.mattscomputertrends.com/harddiskdata.html]. If you haven't ever seen [Matt's Computer Trends|http://www.mattscomputertrends.com/], then you are missing out. According to his site, Matt spends his spare time searching old computer magazines to find historical specs on computer components, and the awesome data he has compiled over the last few years is awesome. reflects this.

Above is a graph depicting the relative capacity of hard disks vs. performance. Comparing performance of hard disks is not completely straightforward, so hard disk transfer rate is measured in KB/s is used. These performance measurements are hard to come by. The transfer rates used here are from an excellent [Tom's Hardware|http://www.tomshardware.com] article that covers [15 years of hard disk performance|http://www.tomshardware.com/reviews/15-years-of-hard-drive-history,1368-7.html] and actually benchmarks the disks to get real performance numbers. While the article is dated from the fall of 2006 and the fastest drive it covers is a 10,000 RPM Western Digital SATA drive, the numbers don't matter much when put on a scale compared to disk capacity. Even if we tossed in a 15,000-RPM SAS drive manufactured in 2008, it the transfer speed would not even be noticeable when compared to with the growth in capacity, and [the Tom's article|http://www.tomshardware.com/reviews/15-years-of-hard-drive-history,1368-7.html] does a good job of driving this point home.

This table above shows the evolution of backup software technology vs. hard disk technology. It also shows the typical number of files found on a server. A real challenge for typical backup software is that they have to examine every file on the server to determine if it has changed. While this examination is done using variety of techniques discussed later, the sheer volume of files that need to be indexed by the backup application is a massive bottleneck. For example, consider that unless you use R1Soft's Continuous Data Protection product, your backup application probably has to walk crawl the entire tree of files on your server. For some servers, this is not that bad. For others, this it is very time consuming. Factor in the time to compute deltas or actually read file data, and it's it is no wonder that we are only back up our servers up on a daily basis without Continuous Data Protection technology.