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Chapter 9. Backups

Table of Contents
9.1. Tape Media
9.2. Backup Programs
9.3. What about backups to floppies?

Issues of hardware compatibility are among the most troublesome in the computer industry today and FreeBSD is by no means immune to trouble. In this respect, FreeBSD's advantage of being able to run on inexpensive commodity PC hardware is also its liability when it comes to support for the amazing variety of components on the market. While it would be impossible to provide a exhaustive listing of hardware that FreeBSD supports, this section serves as a catalog of the device drivers included with FreeBSD and the hardware each drivers supports. Where possible and appropriate, notes about specific products are included. You may also want to refer to the kernel configuration file section in this handbook for a list of supported devices.

As FreeBSD is a volunteer project without a funded testing department, we depend on you, the user, for much of the information contained in this catalog. If you have direct experience of hardware that does or does not work with FreeBSD, please let us know by sending e-mail to the FreeBSD documentation project mailing list . Questions about supported hardware should be directed to the FreeBSD general questions mailing list (see Mailing Lists for more information). When submitting information or asking a question, please remember to specify exactly what version of FreeBSD you are using and include as many details of your hardware as possible.

9.1. Tape Media

The major tape media are the 4mm, 8mm, QIC, mini-cartridge and DLT.

9.1.1. 4mm (DDS: Digital Data Storage)

4mm tapes are replacing QIC as the workstation backup media of choice. This trend accelerated greatly when Conner purchased Archive, a leading manufacturer of QIC drives, and then stopped production of QIC drives. 4mm drives are small and quiet but do not have the reputation for reliability that is enjoyed by 8mm drives. The cartridges are less expensive and smaller (3 x 2 x 0.5 inches, 76 x 51 x 12 mm) than 8mm cartridges. 4mm, like 8mm, has comparatively short head life for the same reason, both use helical scan.

Data thruput on these drives starts ~150kB/s, peaking at ~500kB/s. Data capacity starts at 1.3 GB and ends at 2.0 GB. Hardware compression, available with most of these drives, approximately doubles the capacity. Multi-drive tape library units can have 6 drives in a single cabinet with automatic tape changing. Library capacities reach 240 GB.

4mm drives, like 8mm drives, use helical-scan. All the benefits and drawbacks of helical-scan apply to both 4mm and 8mm drives.

Tapes should be retired from use after 2,000 passes or 100 full backups.

9.1.2. 8mm (Exabyte)

8mm tapes are the most common SCSI tape drives; they are the best choice of exchanging tapes. Nearly every site has an exabyte 2 GB 8mm tape drive. 8mm drives are reliable, convenient and quiet. Cartridges are inexpensive and small (4.8 x 3.3 x 0.6 inches; 122 x 84 x 15 mm). One downside of 8mm tape is relatively short head and tape life due to the high rate of relative motion of the tape across the heads.

Data thruput ranges from ~250kB/s to ~500kB/s. Data sizes start at 300 MB and go up to 7 GB. Hardware compression, available with most of these drives, approximately doubles the capacity. These drives are available as single units or multi-drive tape libraries with 6 drives and 120 tapes in a single cabinet. Tapes are changed automatically by the unit. Library capacities reach 840+ GB.

Data is recorded onto the tape using helical-scan, the heads are positioned at an angle to the media (approximately 6 degrees). The tape wraps around 270 degrees of the spool that holds the heads. The spool spins while the tape slides over the spool. The result is a high density of data and closely packed tracks that angle across the tape from one edge to the other.

9.1.3. QIC

QIC-150 tapes and drives are, perhaps, the most common tape drive and media around. QIC tape drives are the least expensive "serious" backup drives. The downside is the cost of media. QIC tapes are expensive compared to 8mm or 4mm tapes, up to 5 times the price per GB data storage. But, if your needs can be satisfied with a half-dozen tapes, QIC may be the correct choice. QIC is the most common tape drive. Every site has a QIC drive of some density or another. Therein lies the rub, QIC has a large number of densities on physically similar (sometimes identical) tapes. QIC drives are not quiet. These drives audibly seek before they begin to record data and are clearly audible whenever reading, writing or seeking. QIC tapes measure (6 x 4 x 0.7 inches; 15.2 x 10.2 x 1.7 mm). Mini-cartridges, which also use 1/4" wide tape are discussed separately. Tape libraries and changers are not available.

Data thruput ranges from ~150kB/s to ~500kB/s. Data capacity ranges from 40 MB to 15 GB. Hardware compression is available on many of the newer QIC drives. QIC drives are less frequently installed; they are being supplanted by DAT drives.

Data is recorded onto the tape in tracks. The tracks run along the long axis of the tape media from one end to the other. The number of tracks, and therefore the width of a track, varies with the tape's capacity. Most if not all newer drives provide backward-compatibility at least for reading (but often also for writing). QIC has a good reputation regarding the safety of the data (the mechanics are simpler and more robust than for helical scan drives).

Tapes should be retired from use after 5,000 backups.

9.1.5. DLT

DLT has the fastest data transfer rate of all the drive types listed here. The 1/2" (12.5mm) tape is contained in a single spool cartridge (4 x 4 x 1 inches; 100 x 100 x 25 mm). The cartridge has a swinging gate along one entire side of the cartridge. The drive mechanism opens this gate to extract the tape leader. The tape leader has an oval hole in it which the drive uses to "hook" the tape. The take-up spool is located inside the tape drive. All the other tape cartridges listed here (9 track tapes are the only exception) have both the supply and take-up spools located inside the tape cartridge itself.

Data thruput is approximately 1.5MB/s, three times the thruput of 4mm, 8mm, or QIC tape drives. Data capacities range from 10GB to 20GB for a single drive. Drives are available in both multi-tape changers and multi-tape, multi-drive tape libraries containing from 5 to 900 tapes over 1 to 20 drives, providing from 50GB to 9TB of storage.

Data is recorded onto the tape in tracks parallel to the direction of travel (just like QIC tapes). Two tracks are written at once. Read/write head lifetimes are relatively long; once the tape stops moving, there is no relative motion between the heads and the tape.

9.1.6. Using a new tape for the first time

The first time that you try to read or write a new, completely blank tape, the operation will fail. The console messages should be similar to:

    sa0(ncr1:4:0): NOT READY asc:4,1
    sa0(ncr1:4:0):  Logical unit is in process of becoming ready

The tape does not contain an Identifier Block (block number 0). All QIC tape drives since the adoption of QIC-525 standard write an Identifier Block to the tape. There are two solutions:

mt fsf 1 causes the tape drive to write an Identifier Block to the tape.

Use the front panel button to eject the tape.

Re-insert the tape and dump(8) data to the tape.

dump(8) will report DUMP: End of tape detected and the console will show: HARDWARE FAILURE info:280 asc:80,96

rewind the tape using: mt rewind

Subsequent tape operations are successful.