Tape Backup Trials
A Backup Article Contributed by Anand R
Tape Backup Options
Two backup options exist: tape or disk. The simplest method, to back up to floppy disk, is really only suitable for standalone PCs with small hard drives. If a server has few MBs of space then using floppies for disaster recovery is useful. And most servers have at least several hundred megabytes, if not gigabytes, of storage. Backing up to floppies is even marginal for users.
Users have less disk storage than servers do, but its hard for the network administrator to ensure that the users will really back up their data. Most users will back up only after they have lost important data, and then only until they feel invincible again. In practice, it is ridiculous to back up the server to floppies. You can, however, back up the server to another hard disk, either removable or fixed called Disk backup.
Removable disks are handy because if the server or disk fails, you can pop out the damaged equipment and pop in the backup disk. Majority of network administrators back up to tape. Tape is inexpensive, convenient, and widely available. Network managers may complain bitterly about tape and its ills, but basically, it is the backup medium of choice. A new option in the backup bag of tricks is optical disks but they are much more expensive.
Backup Tape Formats
The most common tape format is standardized by the Quarter Inch Committee. The tape is a quarter-inch wide with nine parallel tracks, enclosed in a plastic housing about the size of a VCR tape. 3M's DC600 is the most popular of the formats. A DC600 fits into a standard 5G-inch form factor, so it can be internally mounted in a PC, although the vast majority of drives are attached externally. The standard tape length is 600 feet. The extended length cartridge has 600 feet of tape.
The newer DC2000 format uses the same G-inch nine-track media but the cartridge fits into the 3H-inch form factor, which is perfect for a PS/2. Digital Audio Tape (DAT) is the newest backup medium. DAT for data is the same DAT tape that excites audiophiles. DAT can store several gigabytes of information on a cassette the size of a cigarette pack. DAT will offer terabytes of storage in the future. The difference is DAT uses digital recording. DAT drives use helical scan.
Tape Methods
There is very little difference among the various tape drives. Basically they are made by a small number of manufacturers and resold by companies that make backup software. This venue is currently changing, since the tape drive manufacturers are beginning to sell directly to the end users and dealers. There are two methods of operation: image and file-by-file. Image backup is more primitive and less desirable.
A drive performing an image backup takes a complete image or snapshot of the disk, not concerning itself with the disk's file structure. It just copies all the bits onto tape. Due to this lack of overhead, image backup is fast. But it is not the most efficient. An administrator who wants to restore a single file will have to restore the entire disk, which can take hours. File-by-file backup is far more efficient.
In this method, data from each file is copied to tape before moving onto the next file. It takes longer to reconstruct the fragmented files into whole units, because the disk head has to jump around, but you can restore individual files much more quickly. Also, with file-by-file, you can back up selected files, since only a small percentage of the files are changed each day.
Tape Backup Time
Backup is not effective if you only do it occasionally. It's like exercise. It doesn't matter what you do as long as you do it regularly.A rule of thumb is to back up the files that change every day, and back up the program executables once a week. Then the worst that could happen would be that the users would lose one day's work. But even if you don't take the time to back up every day, at least do a complete backup every week.
