A. A reader sent in the following information regarding offline backups and image backups. You can use any backup program--or even the simple Copy command--to reliably back up files that aren't in use. However, backing up files that are in use, such as system files, when your OS is in an online state can be complicated. Online backup software products, such as Computer Associates' (CA's) BrightStor ARCserve Backup and VERITAS Software's VERITAS Backup Exec, make it difficult or sometimes impossible to restore an entire server or workstation to the identical state it was in when you performed the backup because some files might be open and being accessed by the system. Add-on software agents are available to help back up these open files, but they aren't always reliable. Logically, offline backups provide the highest level of integrity because no files are held open and the system state is flat.

Offline backup software, sometimes called "true image" software, uses another bootable media (e.g., 3.5" disk, CD-ROM) rather than the hard disk to back up servers and workstations while their OSs are inactive. Offline backup products, such as Symantec Ghost and PowerQuest's Drive Image, offer a simple way to back up hard disks, including virtual RAID 5 disks, for servers and workstations that use FAT12, FAT16, FAT32, and NTFS. The software backs up all local hard disks and server or workstation partitions to one file (or to a series of truncated files if you're backing up files larger than 2.1GB and the file system on the disk to which you're backing up the files doesn't recognize file sizes this large). Typically, offline backup software that copies a computer hard disk to another disk, either locally or over a network, will be 5 to 10 times faster than an online backup going to the fastest tape drive. The best features of offline backups are that they let you restore a system to the exact state it was in at the moment you performed the last backup, and you can perform the restore far faster and easier than you can restore from tape.

An image backup is a replica of all the data on your hard disk, including exact file locations, rather than just copies of all your files. After you create an image backup file, you can use third-party tools, such as Drive Image, to restore any file or files from within the image backup file.