An Automated Reliable Backup Solution

These days, it is common to fill huge hard drives with movies, music, videos, software, documents and many other forms of data. Manual backups to CD or DVD often are neglected because of the time-consuming manual intervention necessary to overcome media size limitations and data integrity issues. Hence, most of this data is not backed up on a regular basis. I work as a security professional, specifically in the area of software development. In my spare time, I am an open-source enthusiast and have developed a number of open-source projects. Given my broad spectrum of interests, I have a network in my home consisting of 12 computers, which run a combination of Linux, Mac OS X and Windows. Losing my work is unacceptable!

In order to function in my environment, a backup solution must accommodate multiple users of different machines, running different operating systems. All users must have the ability to back up and recover data in a flexible and unattended manner. This requires that data can be recovered at a granularity ranging from a single file to an entire archive stored at any specified date and time. Because multiple users can access the backup system, it is important to incorporate security functions, specifically data confidentiality, which prevents users from being able to see other users' data, and data integrity, which ensures that the data users recover from backups was originally created by them and was not altered.

In addition to security, reliability is another key requirement. The solution must be tolerant of individual hardware faults. In this case, the component most likely to fail is a hard drive, and therefore the solution should implement hard drive fault tolerance. Finally, the solution should use drive space and network bandwidth efficiently. Efficient use of bandwidth allows more users to back up their data simultaneously. Likewise, if hard drive space is used efficiently by each user, more data can be backed up. A few additional requirements that I impose on all of my projects are that they be visually attractive, of an appropriate size and reasonably priced.

I first attempted to find an existing solution. I found a number of solutions that fit into two categories: single-drive network backup appliances and RAID array network backup appliances. A prime example of a solution in the first category is the Western Digital NetCenter product. All of the products I found in this category failed in most, if not all, of the functionality, security, reliability and performance requirements. The appliances found in the second category are generally designed for enterprise use rather than personal use. Hence, they tend to be much more expensive than those found in the first category. The Snap Server 2200 is an example of one of the lower-end versions of an appliance that fits under the second category. It generally sells for about $1,000 US with a decent amount of hard drive space. The products I found in category two also failed in most, if not all, of the functionality, security, performance and general requirements.

Due to the excessive cost and requirements issues of the readily available solutions, I decided to build my own unattended, encrypted, redundant, network-based backup solution using Linux, Duplicity and commercial off-the-shelf (COTS) hardware. Using these tools allowed me to create a network appliance that could make full and incremental backups, which are both encrypted and digitally signed. Incremental backups are backups in which only the changes since the last backup are saved. This reduces both the required storage and the required bandwidth for each backup. Full backups are backups in which the complete files, rather than just the changes, are backed up. These tools also provided the capability of restoring both entire archives and single files backed up at a specified time. For, example, suppose I recently received a virus, and I know that a week ago I did not have the virus. This solution would easily allow me to restore my system as it was one week ago, or two months ago, or as far back as my first backup.

Figure 1. Silver Venus 668 Case (Front)

Duplicity, according to its project Web page, is a backup utility that backs up directories by encrypting tar-format volumes and uploading them to a remote or local file server. Duplicity, the cornerstone of this solution, is integrated with librsync, GnuPG and a number of file transport mechanisms. Duplicity provides a mechanism that meets my functionality, security and performance requirements.

Duplicity first uses librsync to create a tar-format volume consisting of either a full backup or an incremental backup. Then it uses GnuPG to encrypt and digitally sign the tar-format volume, providing the data confidentiality and integrity required. Once the tar-format volume is encrypted and signed, Duplicity transfers the backups to the specified location using one of its many supported file transportation mechanisms. In this case, I used the SSH file transportation mechanism, because it assures that the backups are encrypted while in transit. This is not necessary, as the backups are encrypted and signed prior to being transported, but it does add another layer of protection and complexity for someone trying to break in to the system. Furthermore, SSH is a commonly used service that eliminates the need to install another service, such as FTP, NFS or rsync.

Figure 2. Silver Venus 668 Case (Back)