Keeping laptop backups in sync

Backing up laptops and keeping them in sync with desktops and servers doesn't have to be torture if you follow these procedures.

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 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 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.

Back up your own
If you use Windows 2000 or XP, familiarize yourself with Offline Files. This feature - introduced in Windows 2000 - provides a centralized backup of several users' desktops or laptops to one desktop. Suppose you have a laptop, and you want to back up of all of your documents to the desktop. You must first colocate your documents and copy them to a directory on the desktop. Then create a Windows share of that directory back to the laptop. It makes things easier if you assign a drive letter to it. On the laptop, right click on the network share and select "Make Available Offline." Click OK, and Windows makes a local copy of all documents in that network share.

You're now free to work on these documents on your desktop or laptop. By default, changes on either machine will be synchronized when you log off of your laptop. You can change these preferences to synchronize on a regular basis, or to synchronize when you log on to your laptop. You can also force synchronization at any time. If there's ever a conflict with a file that has been changed on your desktop and laptop, Windows will ask you what you want to do. You have the option of overwriting either file or copying both files to both machines with a notation (e.g., copy 2). If you do a good job of keeping your important documents on this offline drive, the deletion or corruption of files can be corrected by synchronizing again.

I encountered one challenge when attempting to use this in my environment. To completely remove all backup requirements from my laptop, I needed to synchronize three types of files. The first type was word processing documents and spreadsheets. The second was a Palm Pilot database, and the third were my Outlook .pst files. With Outlook, I wanted to use the same .pst file on the road that I had available in the office. With my Palm Pilot, I wanted to sync it to my desktop when I was in the office and to my laptop when I was on the road. The idea was that I would arrive at my office after having been on the road, synchronize my Offline Files, put away my laptop and continue to use Outlook, with my Palm Pilot cradle and all other documents on my desktop as if I had never left the office. The problem was that - by default - Windows excludes files with a .pst or .db extension from synchronization. I found a workaround to this problem.

I found the answer in a Microsoft article. You can go here to read this article about the gpedit.msc command, and how you can use it to change extensions not synchronized by Offline Files. While using it to synchronize .pst between multiple computers is unsupported, it worked fine for me. I had to ensure I synchronized from my laptop to my desktop before using Outlook on my desktop. Otherwise, I would have ended up with new mail in both .pst files. Recovering from this wasn't pretty.

I now have every bit of needed data on my laptop when I travel - without needing to back it up. I can even share these documents with others in the office who need to work on them while I'm on the road. When I come back to the office, I synchronize my Offline Files and put my laptop away. Any documents I've changed while on the road are automatically copied to my desktop, and any documents that anyone else has changed while I was on the road get copied to my laptop. This includes all of my Outlook mail and my Palm Pilot database. Before going on the road again, I make sure I synchronize my laptop again.

The Linux solution
Users of Linux desktops and laptops also have a free option available to them - rsync, a file transfer program for Unix systems - which uses the rsync algorithm that provides a fast method for bringing remote files into sync. It does this by sending just the differences in the files across the link, without requiring that both sets of files are present at one of the ends of the link beforehand. It can be used to update whole directory trees and file systems, and can even preserve symbolic links, hard links, file ownership, permissions, devices and times. It requires no special privileges to install and it can use rsh, ssh or direct sockets as the transport. It even supports anonymous rsync, which is ideal for mirroring.

With rsync, establish synchronization between your laptop and any Unix or Linux desktop where you have a home directory. This gives you the same amount of functionality as described in the Windows solution earlier. Using one of these utilities, you can backup laptops and other remote users. All you need is a central place for everyone to synchronize to.

Web Bonus:
Online resources from "Mobile computers: Regular backups prevent disaster," by Linda Christie.

This was last published in January 2003

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