A look at online storage and back-up services.Files, files, where are your files? If you move around from office to office, the best place to keep them could be with an online storage or back-up service.There are two approaches: store and share your files online, or back up all your computer data. Folder-replicating services synchronize the online folder with local clients running the proper software.One reader\u00a0runs a service based on Novell's\u00a0iFolder utility. Novell\u2019s gotten good reviews for this service, even by me in the past. Recently it extended the server options beyond NetWare to Linux and Windows 2000. Unfortunately for all Novell\u2019s talk about Linux desktops, there\u2019s still no Linux client for iFolder. But Windows clients can use the service, through a company server or a service, and it will keep the files synchronized between the server and all clients configured to use that particular server folder.When you configure your primary data storage folder as the iFolder contact point, you essentially have a backup of all your data. Products from\u00a0SwapDrive\u00a0($15 monthly for 250M bytes) and\u00a0FolderShare\u00a0($5.90 monthly per user for unlimited storage) work similarly. Check out others through directories such as\u00a0Yahoo.com\u00a0and the\u00a0Open Directory Project.If sharing files among multiple people is important, you want to verify you can have private and shared folders. You'll have to create user names with access rights for each user, but that lets you keep private files private, yet share files you want. Folder-sharing services tend to make these type of arrangements easier than the back-up service vendors do, but check to verify. FolderShare offers good support for sharing a set of folders among multiple users.SwapDrive offers some interesting options. WhaleMail bypasses the attachment-size limitations on some e-mail servers by holding the files on its system and sending notice to the intended recipient. The file destination target user then chooses when to download the file to his hard disk rather than through an e-mail download. Compression, security and notifications are part of the service. If you're ever cursed someone who sent a 9.87M-byte PowerPoint presentation as you wait for your laptop on a hotel dial-up connection, you know WhaleMail could come in handy. Get the notice, breathe a sigh of relief, and download the file when you get back home to your broadband connection.Personally, I'm paranoid about losing files and want back-up security as well as file storage. There are plenty of back-up services that work by running a small application on your computer that sends files to your online storage automatically whenever the files change or when you schedule a backup.See if your back-up service of choice offers file versioning, meaning it keeps several versions of the same document. If your folder sharing or back-up service overwrites files, the original will be gone quickly.\u00a0Backup Solutions\u00a0($6.95 per month for 250M bytes, up to 10G bytes for $25 per month) offers 10 versions, while folder synchronization services almost never provide versioning.