For a lot of people these days, the data they create and store on their computers is worth more than the hardware itself -- especially if you factor in the sentimental value of years of collected e-mail and photos.

That's why regular and complete backups of your personal files are so important. You can replace hardware and reload software, but rewriting your novel-in-progress or redoing your previous five years' financial data is a lot harder. The trick, though, is to find some backup system that doesn't feel like a chore -- ideally, one that you don't know is there at all.

The Mirra Personal Server 2.0 pulls that trick off with a combination of hardware, software and Web-based tools that allow both continuous backups -- and remote access to all of your backed-up data. Mirra is a simple, straightforward system to operate. But it's definitely not cheap.

Mirra's Personal Servers cost $399, $499 and $749 in 80-, 120- and 250-gigabyte sizes. Each consists of a small tower case that connects via Ethernet cable to a hub or router on your home's network. It looks much like a standard desktop PC, except for the lack of keyboard, mouse and monitor and the blocked-off connectors on the back.

You can usually expect any computing device with "server" in its name to be excruciatingly difficult to set up, but that's not the case with the Mirra. Plug in its power and Ethernet cables, hit a switch and it's up and running. Then install Mirra's backup software (Win 2000 or newer) on each computer on the network, which took about 10 minutes per machine in our test.

Once loaded, Mirra's software will offer to back up a standard set of file locations -- your My Documents folder, your Internet Explorer favorites and your Microsoft Outlook mail, contacts and calendar data. (The invisible Application Data directory, a common hiding place for such data as non-Microsoft Web bookmarks and mailbox files, isn't included in Mirra's default backup set, but it should be.) You can also add other folders to the backup list, but not individual files.

The Mirra server (which runs on a version of Linux) then copies your data as fast as your network can push it -- roughly 20 to 30 minutes per gigabyte of data on a typical WiFi network.

After the initial transfer, Mirra pretty much disappears. It silently and invisibly copies any new or changed files in your designated backup spots -- while keeping the last seven preceding versions of any one file. And it does this constantly, not just once a day or once a week.

Mirra's desktop software allows quick access to backup settings, the status of your backups, restoration of lost files -- and its file-sharing features.

The Personal Server can make selected data available across your home network and the Internet at large, via a password-protected login on Mirra's Web site ( You, and anyone you designate, can upload and download files to and from your server through this Web gateway, and Mirra's system can then automatically copy them to the computers on your home network.

Mirra's Web services -- free for buyers to use -- also extend to online photo sharing and a shared address book, but neither feature is that remarkable. The photo option doesn't include photo printing services, and the address book feature seems like an afterthought, unable to compete with dedicated address book programs.

For many users, Mirra makes no sense -- if you don't have a home network, or one of the computers on it is running anything older than Win 2000, or any non-Microsoft operating system, Mirra will be wasted capacity. Even for those whose networks do line up appropriately, Mirra still costs far more than CD or DVD backup, or even external hard drives such as the Maxtor OneTouch we've reviewed favorably here.

But what it offers that those competing methods don't is certainty. As long as the electricity stays on, your files will be backed up effortlessly.

Mirra makes backups a no-brainer -- at a price.