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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta name="generator" content="HTML Tidy, see www.w3.org" /><title>Creating and Using Data Tapes</title><meta name="GENERATOR" content="Modular DocBook HTML Stylesheet Version 1.7" /><link rel="HOME" title="FreeBSD Handbook" href="index.html" /><link rel="UP" title="Storage" href="disks.html" /><link rel="PREVIOUS" title="Creating and Using Floppy Disks" href="floppies.html" /><link rel="NEXT" title="Backups to Floppies" href="backups-floppybackups.html" /><link rel="STYLESHEET" type="text/css" href="docbook.css" /></head><body class="SECT1" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#840084"alink="#0000FF"><div class="NAVHEADER"><table summary="Header navigation table" width="100%" border="0" cellpadding="0"cellspacing="0"><tr><th colspan="3" align="center">FreeBSD Handbook</th></tr><tr><td width="10%" align="left" valign="bottom"><a href="floppies.html"accesskey="P">Prev</a></td><td width="80%" align="center" valign="bottom">Chapter 16 Storage</td><td width="10%" align="right" valign="bottom"><a href="backups-floppybackups.html"accesskey="N">Next</a></td></tr></table><hr align="LEFT" width="100%" /></div><div class="SECT1"><h1 class="SECT1"><a id="BACKUPS-TAPEBACKUPS" name="BACKUPS-TAPEBACKUPS">16.9 Creatingand Using Data Tapes</a></h1><p>The major tape media are the 4mm, 8mm, QIC, mini-cartridge and DLT.</p><div class="SECT2"><h2 class="SECT2"><a id="BACKUPS-TAPEBACKUPS-4MM" name="BACKUPS-TAPEBACKUPS-4MM">16.9.14mm (DDS: Digital Data Storage)</a></h2><p>4mm tapes are replacing QIC as the workstation backup media of choice. This trendaccelerated 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 havethe reputation for reliability that is enjoyed by 8mm drives. The cartridges are lessexpensive 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 helicalscan.</p><p>Data throughput on these drives starts ~150 kB/s, peaking at ~500 kB/s. Datacapacity starts at 1.3 GB and ends at 2.0 GB. Hardware compression, availablewith most of these drives, approximately doubles the capacity. Multi-drive tape libraryunits can have 6 drives in a single cabinet with automatic tape changing. Librarycapacities reach 240 GB.</p><p>The DDS-3 standard now supports tape capacities up to 12 GB (or 24 GBcompressed).</p><p>4mm drives, like 8mm drives, use helical-scan. All the benefits and drawbacks ofhelical-scan apply to both 4mm and 8mm drives.</p><p>Tapes should be retired from use after 2,000 passes or 100 full backups.</p></div><div class="SECT2"><h2 class="SECT2"><a id="BACKUPS-TAPEBACKUPS-8MM" name="BACKUPS-TAPEBACKUPS-8MM">16.9.28mm (Exabyte)</a></h2><p>8mm tapes are the most common SCSI tape drives; they are the best choice of exchangingtapes. Nearly every site has an Exabyte 2 GB 8mm tape drive. 8mm drives arereliable, convenient and quiet. Cartridges are inexpensive and small (4.8 x 3.3 x 0.6inches; 122 x 84 x 15 mm). One downside of 8mm tape is relatively short head and tapelife due to the high rate of relative motion of the tape across the heads.</p><p>Data throughput ranges from ~250 kB/s to ~500 kB/s. Data sizes start at300 MB and go up to 7 GB. Hardware compression, available with most of thesedrives, approximately doubles the capacity. These drives are available as single units ormulti-drive tape libraries with 6 drives and 120 tapes in a single cabinet. Tapes arechanged automatically by the unit. Library capacities reach 840+ GB.</p><p>The Exabyte ``Mammoth'' model supports 12 GB on one tape (24 GB withcompression) and costs approximately twice as much as conventional tape drives.</p><p>Data is recorded onto the tape using helical-scan, the heads are positioned at anangle to the media (approximately 6 degrees). The tape wraps around 270 degrees of thespool that holds the heads. The spool spins while the tape slides over the spool. Theresult is a high density of data and closely packed tracks that angle across the tapefrom one edge to the other.</p></div><div class="SECT2"><h2 class="SECT2"><a id="BACKUPS-TAPEBACKUPS-QIC" name="BACKUPS-TAPEBACKUPS-QIC">16.9.3QIC</a></h2><p>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 thecost of media. QIC tapes are expensive compared to 8mm or 4mm tapes, up to 5 times theprice 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 <span class="emphasis"><iclass="EMPHASIS">most</i></span> common tape drive. Every site has a QIC drive of somedensity or another. Therein lies the rub, QIC has a large number of densities onphysically similar (sometimes identical) tapes. QIC drives are not quiet. These drivesaudibly 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).</p><p>Data throughput ranges from ~150 kB/s to ~500 kB/s. Data capacity rangesfrom 40 MB to 15 GB. Hardware compression is available on many of the newer QICdrives. QIC drives are less frequently installed; they are being supplanted by DATdrives.</p><p>Data is recorded onto the tape in tracks. The tracks run along the long axis of thetape media from one end to the other. The number of tracks, and therefore the width of atrack, varies with the tape's capacity. Most if not all newer drives providebackward-compatibility at least for reading (but often also for writing). QIC has a goodreputation regarding the safety of the data (the mechanics are simpler and more robustthan for helical scan drives).</p><p>Tapes should be retired from use after 5,000 backups.</p></div><div class="SECT2"><h2 class="SECT2"><a id="BACKUPS-TAPEBACKUPS-DLT" name="BACKUPS-TAPEBACKUPS-DLT">16.9.4DLT</a></h2><p>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 25mm). The cartridge has a swinging gate along one entire side of the cartridge. The drivemechanism opens this gate to extract the tape leader. The tape leader has an oval hole init which the drive uses to ``hook'' the tape. The take-up spool is located inside thetape drive. All the other tape cartridges listed here (9 track tapes are the onlyexception) have both the supply and take-up spools located inside the tape cartridgeitself.</p><p>Data throughput is approximately 1.5 MB/s, three times the throughput of 4mm,8mm, or QIC tape drives. Data capacities range from 10 GB to 20 GB for a singledrive. Drives are available in both multi-tape changers and multi-tape, multi-drive tapelibraries containing from 5 to 900 tapes over 1 to 20 drives, providing from 50 GBto 9 TB of storage.</p><p>With compression, DLT Type IV format supports up to 70 GB capacity.</p><p>Data is recorded onto the tape in tracks parallel to the direction of travel (justlike QIC tapes). Two tracks are written at once. Read/write head lifetimes are relativelylong; once the tape stops moving, there is no relative motion between the heads and thetape.</p></div><div class="SECT2"><h2 class="SECT2"><a id="AEN24681" name="AEN24681">16.9.5 AIT</a></h2><p>AIT is a new format from Sony, and can hold up to 50 GB (with compression) pertape. The tapes contain memory chips which retain an index of the tape's contents. Thisindex can be rapidly read by the tape drive to determine the position of files on thetape, instead of the several minutes that would be required for other tapes. Softwaresuch as <b class="APPLICATION">SAMS:Alexandria</b> can operate forty or more AIT tapelibraries, communicating directly with the tape's memory chip to display the contents onscreen, determine what files were backed up to which tape, locate the correct tape, loadit, and restore the data from the tape.</p><p>Libraries like this cost in the region of $20,000, pricing them a little out of thehobbyist market.</p></div><div class="SECT2"><h2 class="SECT2"><a id="AEN24689" name="AEN24689">16.9.6 Using a New Tape for the FirstTime</a></h2><p>The first time that you try to read or write a new, completely blank tape, theoperation will fail. The console messages should be similar to:</p><pre class="SCREEN">sa0(ncr1:4:0): NOT READY asc:4,1sa0(ncr1:4:0): Logical unit is in process of becoming ready</pre><p>The tape does not contain an Identifier Block (block number 0). All QIC tape drivessince the adoption of QIC-525 standard write an Identifier Block to the tape. There aretwo solutions:</p><ul><li><p><tt class="COMMAND">mt fsf 1</tt> causes the tape drive to write an Identifier Blockto the tape.</p></li><li><p>Use the front panel button to eject the tape.</p><p>Re-insert the tape and <tt class="COMMAND">dump</tt> data to the tape.</p><p><tt class="COMMAND">dump</tt> will report ``<tt class="ERRORNAME">DUMP: End of tapedetected</tt>'' and the console will show: ``<tt class="ERRORNAME">HARDWARE FAILUREinfo:280 asc:80,96</tt>''.</p><p>rewind the tape using: <tt class="COMMAND">mt rewind</tt>.</p><p>Subsequent tape operations are successful.</p></li></ul></div></div><div class="NAVFOOTER"><hr align="LEFT" width="100%" /><table summary="Footer navigation table" width="100%" border="0" cellpadding="0"cellspacing="0"><tr><td width="33%" align="left" valign="top"><a href="floppies.html"accesskey="P">Prev</a></td><td width="34%" align="center" valign="top"><a href="index.html"accesskey="H">Home</a></td><td width="33%" align="right" valign="top"><a href="backups-floppybackups.html"accesskey="N">Next</a></td></tr><tr><td width="33%" align="left" valign="top">Creating and Using Floppy Disks</td><td width="34%" align="center" valign="top"><a href="disks.html"accesskey="U">Up</a></td><td width="33%" align="right" valign="top">Backups to Floppies</td></tr></table></div><p align="center"><small>This, and other documents, can be downloaded from <ahref="ftp://ftp.FreeBSD.org/pub/FreeBSD/doc/">ftp://ftp.FreeBSD.org/pub/FreeBSD/doc/</a>.</small></p><p align="center"><small>For questions about FreeBSD, read the <ahref="http://www.FreeBSD.org/docs.html">documentation</a> before contacting <<ahref="mailto:questions@FreeBSD.org">questions@FreeBSD.org</a>>.<br />For questions about this documentation, e-mail <<ahref="mailto:doc@FreeBSD.org">doc@FreeBSD.org</a>>.</small></p></body></html>⌨️ 快捷键说明
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