Backing Up a Small Network

To this point, I've assumed that you're backing up a single Mac. But what if you have several in your home or office? How does this affect your backup strategy?

One approach is to back up each machine separately. This may involve keeping separate stacks of recordable CDs or DVDs next to each machine, or hooking up external FireWire drives to each one (though you could, of course, move a single high-capacity drive from one computer to the next). If your backup needs are relatively small, there's nothing wrong with this approach. But if you have more than a couple of machinesespecially if their hard disks contain a lot of data that you can't afford to losea wiser strategy would be to back them all up at the same time over your network.


You do have a network, right? If you have multiple machines that aren't currently connected (whether by Ethernet cabling or AirPort wireless networking), you should hook them up. Not only does a network enable better backups, it makes transferring files and accessing the Internet much easier.

Network Backup Approaches

In a network backup, one computer functions as the backup server. This is the machine to which your backup device(s) are physically connected. Files from your other machines are copied over the network onto each backup device. Network backups can proceed by three different methods:

  • The server shares its backup volume (using AFP, FTP, or SMB; see the Glossary for info on these acronyms), which the client machines mount as a volume in the Finder. Then each client machine uses its own backup application to back up files to the network volume (rather than a locally attached hard drive or optical drive). This is sometimes called a push backup, as each client "pushes" its data onto the network volume.

  • Each client machine shares its hard disk (again, using AFP, FTP, or SMB). The server mounts each of these volumes in the Finder, and then the single copy of the backup application running on the server copies files from each of the network volumes onto its locally attached backup volume. This is sometimes called a pull backup, as the server "pulls" data from each of the clients onto its backup volumes.

  • The server runs backup software that supports client-server network backups, and the other machines run client software that communicates with the server directlywithout any of the machines having to share or mount volumes.


Some SMB servers limit the size of any single file to 2 GB; others limit it to 4 GB; still others have limits as high as 2 TB. Because some backup software transmits all your data over the network as a single file, you may run into situations where you cannot back up more than 2 GB (or 4 GB) of data to an SMB server. If you can't persuade your system administrator to update the server software to a version that supports larger file sizes, you may need to use a different server (or different backup software).

Almost all backup applications support push and pull network backups, but I recommend against them. For one thing, network volumes can become disconnected for any number of reasons, and if a volume is unavailable when it's time for a scheduled backup, that backup will fail. A few applications can try to mount missing volumes for you (even remembering user names and passwords, if necessary), but even this is no guarantee of success. Push and pull backups are also inherently less secure than client-server backups, and are sometimes quite slow. Also, in the case of pull backups, file ownership may change in unacceptable ways, making bootable backups impossible. Sometimes push backups can be bootable, but it's a dicey operation.

True client-server backups require less effort, are more secure, and tend to offer more flexibility. Often, client-server backup software also supports multiple platforms. Of the backup software covered in this book, Retrospect, RsyncX, and BackupSW offer client-server backups. Retrospect and BackupSW both support Mac OS X and Windows; Retrospect also supports Mac OS 9, while BackupSW also supports Linux.

If you need to back up a small Macintosh or Macintosh/Windows network, I recommend Retrospect Desktop, which includes a license to back up the machine on which it's installed, plus two more client computers (additional client licenses are available at $37 each, with volume discounts if purchased in packs of 5, 10, 50, or 100). You'll get the best results with the Backup Server script (see Set Up a Backup Server Script, page 200), using hard disks that are large enough for all the data on all the Macs (see Does Size Matter?, page 118).

Special Considerations

Besides selecting the right software, several other matters require your attention when planning a network backup system:

  • Media: Although optical media or other removable storage may be acceptable for single-machine backups, for best results, network backups require storage devices that are always available. In other words, hard drives are the best bet for small networks. (See Chapter 10.) Also, if you're making duplicates that you may later wish to boot from, be sure to partition the hard disks in such a way that each startup disk on the network gets its own partition for a duplicate.

  • Bandwidth: You can perform a network backup using an AirPort wireless network, but even with AirPort Extreme, you get only a small percentage of the bandwidth that a wired 100Base-T Ethernet connection will give youso backups will take much longer, especially if you're duplicating an entire hard disk. In any case, you definitely want the highest-bandwidth network connection you can get. If your computer uses multiple network interfaces, open System Preferences, go to the Network pane, and choose Network Port Configurations from the Show pop-up menu. In the list that appears, drag Built-in Ethernet to the top and click Apply Now to ensure that the wired network is used in preference to AirPort when both are available.


    Every network is different, but I have seen cases where Retrospect client-server backups are unreliable when the client machines' IP addresses are dynamically assigned by an AirPort base station. If this happens to you, consider assigning (private) static IP addresses to each client.

  • Availability: For a scheduled network backup to occur, both server and client machines must be turned on and awake. If your machines are currently not left on all the time, check the Energy Saver pane in System Preferences on each computer to ensure that it will not be off or asleep when backups occur. (For more info, read the sidebar Power Management and Backups, page 171.)


Scheduling network backups for times when all machines are available can be a challengeparticularly if you have laptop computers that are not always on the network. Retrospect offers a great feature called Backup Server that constantly polls all the clients on a network. If it sees one that hasn't been backed up in at least 24 hours (or a period of time you specify), it performs the backup right away. That way, you needn't set up an exact schedule for each machine. Backup Server can be restricted to run only during certain hours on certain days, and it can also use any available, designated hard disk as a destinationso you don't need to figure out in advance when to swap media (for more information, read Set Up a Backup Server Script, page 200).

Remote Backups

In the discussion so far, I've assumed that the machines you need to back up are connected to the same local network as your backup server. But what if you travel frequently with a laptop? Can you use a broadband connection at a hotel or Internet café to copy the files to your server over the Internet? The short answer is: Maybe.

"Push" backups work only if you can mount your backup server's volumes remotely; "pull" backups work only if your server can mount your laptop's volume remotely. Sometimes this works, but often notyour firewall at home must enable access to the necessary ports, and the ISP providing your remote access must also permit file-sharing access over their network. You also run a certain risk that your files may be intercepted in transit by a hacker, unless you take extra steps to encrypt the network link between your laptop and your server.

Client-server backup software, such as Retrospect, normally polls only the local network for available clients. In some casesfor example, with the more-expensive Retrospect Workgroup or Retrospect Server packagesyou can manually enter an IP address for a computer outside your local network. However, if you're traveling and don't know what IP address you'll have at any given time, this method is problematic. One possible solution is to use a dynamic DNS service, such as the one provided by easyDNS (, to assign your laptop a domain name whose IP address changes as needed, and then enter that domain name in Retrospect.

This problem is more readily solvable using a VPN (virtual private network) connection to your home network, but the details of setting up such a system go beyond what I can cover in this book. As a lower-tech workaround, consider packing some DVD-R media for temporary backups when you're on the roadand be sure to store the discs separately from your laptop!

Real World Mac Maintenance and Backups. Industrial-Strength Techniques
Real World Mac Maintenance and Backups. Industrial-Strength Techniques
Year: 2004
Pages: 144 © 2008-2017.
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