Keeping laptop backups in sync

A significant amount of American companies' intellectual property exists on laptops and desktops that aren't being properly backed up - if they're being backed up at all. Two myths are allowing this condition to exist. First, IT decision-makers don't realize how much data resides on unprotected laptops and desktops.

Second, they perceive that backing up desktops and laptops isn't easy to do - or even impossible. This article attempts to debunk both of these myths, especially the second one. It will also include two methods that an individual user can use to easily and automatically create a backup for their machine. I'll also discuss one method for Linux and one for Windows users.

When discussing the possibility of backing up desktops or laptops, a common response from IT management may be: "We don't back up the C: drive on desktops or laptops. Users should save anything important onto the H: drive. We back up that server."

There are many flaws with this methodology - the biggest is human nature. If your desktop runs Windows, it takes extra effort to save files to a network drive. While some Microsoft applications can save files elsewhere, many applications default to the "My Documents" directory. Users must perform an extra step to save the files in the appropriate location. Some applications - such as Outlook - always want to save files in a particular location, resulting in many important files being saved locally.

Network drives can be slower

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than a local drive, causing users to save the working copy of their documents locally. Their intention is to copy the file to the network drive once they are done, but this is often forgotten. Again, many important files - especially current versions of those files - are saved locally on the users' desktop.

Linux and Unix users don't have this problem - Unix has a home directory that can reside anywhere. This is the default location for new files. Even so, some files - especially large files - don't perform well when stored on an NFS server. NFS file systems aren't available if users aren't connected to the corporate LAN. For these reasons, some Unix users store some of their files locally.

Eliminate full backups
What's an IT manager to do? Backing up desktops is problematic. What about laptops? It isn't reasonable to expect a remote user to perform a full backup. A full backup of a 20GB hard drive over a 56Kb connection would take forever. It isn't reasonable to expect a local user to perform a full backup on a regular basis if they don't have a direct connection to your corporate backbone. They could be competing for bandwidth with hundreds - or thousands - of other desktops needing backup.

Therefore, the key to success when backing up desktops and laptops is to eliminate occasional full backups and to reduce the amount of data transferred during incremental backups. If you're willing to spend some money to protect your laptops and desktops, there are a number of commercial products that can help you.

The first challenge these products face is how to eliminate occasional full backups. Attempting to accomplish this with a traditional tape-based product isn't easy. Over time, a complete restore may require hundreds of tapes. To overcome this, a tape-based system using an incremental forever backup methodology must regularly copy the data from many mostly empty older tapes to a smaller subset of newer tapes. This is why most backup products aimed at the desktop and laptop market have opted for disk-based backups. When the backups reside on disk, it's irrelevant how many incremental backups need to be loaded in order to restore a complete system.

Incremental backups
How do we significantly reduce the amount of bandwidth required for incremental backups? Many vendors have attempted to solve this through a technique often referred to as delta block or block-level incremental backups. In this method when a file changes in any way, (e.g., adding one line to your resume) the file's modification time changes. A typical backup and recovery system would then back up that entire file during an incremental backup - even though only a small portion of that file has changed. A block-level incremental backup would also recognize that the file has changed - based on its modification time - but would then determine exactly which blocks in the file have changed, and then back up only those blocks. This technique significantly reduces the amount of data that needs to be transferred to the backup server, as well as the amount of data that must be stored on disk on the backup server. Clearly, combining block-level incremental backups with an incremental-forever backup methodology makes backing up to disk even more important.

Some products perform an additional step aimed at reducing the amount of data that must be transferred during a backup. Ask yourself a question: How many copies of command.com need to be backed up? If a given file has already been backed up from another client, wouldn't it make sense to note that you found another occurrence of the file? It makes sense to only back up each file once, regardless of how many systems where that file resides. This technique is referred to as redundant file elimination.

There are several commercial products designed specifically to back up desktops and laptops. A directory of them may be found here.

A new company called Avamar Technologies, Irvine, CA, combines the functionality provided by block-level incremental backups and redundant file into a single concept - redundant block elimination. Their product, Axion, finds logical sequences in files, objects and databases and stores each unique logical sequence only once per Axion backup system. As a result, edited files, copied attachments, applications replicated across systems and even daily changing databases require an extremely small amount of backup storage. While this particular article is about desktop and laptop backups, Avamar has applied this unique concept to the world of server backup as well.

What if you're only one user or a small company with a limited budget? Although the solutions for such environments may not have equivalent functionality to the products described above, there are solutions available - most of them in the form of replication.

This was first published in January 2003

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