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9.4. Block Devices (Are Gone)
Other UNIX® systems may support a second type of disk device known as block devices. Block devices are disk devices for which the kernel provides caching. This caching makes block-devices almost unusable, or at least dangerously unreliable. The caching will reorder the sequence of write operations, depriving the application of the ability to know the exact disk contents at any one instant in time.
This makes predictable and reliable crash recovery of on-disk data structures (filesystems, databases, etc.) impossible. Since writes may be delayed, there is no way the kernel can report to the application which particular write operation encountered a write error, this further compounds the consistency problem.
For this reason, no serious applications rely on block devices, and in fact, almost all applications which access disks directly take great pains to specify that character (or "raw") devices should always be used. As the implementation of the aliasing of each disk (partition) to two devices with different semantics significantly complicated the relevant kernel code, FreeBSD dropped support for cached disk devices as part of the modernization of the disk I/O infrastructure.
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9.4。块设备（不见了）
其他UNIX®系统可能支持第二种类型的磁盘设备，称为块设备。块设备是内核为其提供缓存的磁盘设备。这种缓存使块设备几乎不可用，或者至少不可靠。缓存将对写入操作的顺序进行重新排序，从而使应用程序无法及时地在任何一个瞬间知道确切的磁盘内容。
这使得磁盘上数据结构（文件系统、数据库等）的可预测和可靠崩溃恢复变得不可能。由于写入可能会延迟，因此内核无法向应用程序报告哪个特定写入操作遇到写入错误，这进一步加剧了一致性问题。
因此，没有严重的应用程序依赖于块设备，事实上，几乎所有直接访问磁盘的应用程序都会煞费苦心地指定应始终使用字符（或“原始”）设备。由于将每个磁盘（分区）的别名实现为具有不同语义的两个设备，显著地使相关内核代码复杂化，因此FreeBSD放弃了对缓存磁盘设备的支持，这是磁盘I/O基础架构现代化的一部分。
Other UNIX® systems may support a second type of disk device known as block devices. Block devices are disk devices for which the kernel provides caching. This caching makes block-devices almost unusable, or at least dangerously unreliable. The caching will reorder the sequence of write operations, depriving the application of the ability to know the exact disk contents at any one instant in time.
This makes predictable and reliable crash recovery of on-disk data structures (filesystems, databases, etc.) impossible. Since writes may be delayed, there is no way the kernel can report to the application which particular write operation encountered a write error, this further compounds the consistency problem.
For this reason, no serious applications rely on block devices, and in fact, almost all applications which access disks directly take great pains to specify that character (or "raw") devices should always be used. As the implementation of the aliasing of each disk (partition) to two devices with different semantics significantly complicated the relevant kernel code, FreeBSD dropped support for cached disk devices as part of the modernization of the disk I/O infrastructure.
------
9.4。块设备（不见了）
其他UNIX®系统可能支持第二种类型的磁盘设备，称为块设备。块设备是内核为其提供缓存的磁盘设备。这种缓存使块设备几乎不可用，或者至少不可靠。缓存将对写入操作的顺序进行重新排序，从而使应用程序无法及时地在任何一个瞬间知道确切的磁盘内容。
这使得磁盘上数据结构（文件系统、数据库等）的可预测和可靠崩溃恢复变得不可能。由于写入可能会延迟，因此内核无法向应用程序报告哪个特定写入操作遇到写入错误，这进一步加剧了一致性问题。
因此，没有严重的应用程序依赖于块设备，事实上，几乎所有直接访问磁盘的应用程序都会煞费苦心地指定应始终使用字符（或“原始”）设备。由于将每个磁盘（分区）的别名实现为具有不同语义的两个设备，显著地使相关内核代码复杂化，因此FreeBSD放弃了对缓存磁盘设备的支持，这是磁盘I/O基础架构现代化的一部分。
In FreeBSD, cdrecord can be used to burn CDs. This command is installed with the sysutils/cdrtools package or port.
While cdrecord has many options, basic usage is simple. Specify the name of the ISO file to burn and, if the system has multiple burner devices, specify the name of the device to use:
# cdrecord dev=device imagefile.iso
To determine the device name of the burner, use -scanbus which might produce results like this:
# cdrecord -scanbus
ProDVD-ProBD-Clone 3.00 (amd64-unknown-freebsd10.0) Copyright (C) 1995-2010 Jörg Schilling
Using libscg version 'schily-0.9'
scsibus0:
0,0,0 0) 'SEAGATE ' 'ST39236LW ' '0004' Disk
0,1,0 1) 'SEAGATE ' 'ST39173W ' '5958' Disk
0,2,0 2) *
0,3,0 3) 'iomega ' 'jaz 1GB ' 'J.86' Removable Disk
0,4,0 4) 'NEC ' 'CD-ROM DRIVE:466' '1.26' Removable CD-ROM
0,5,0 5) *
0,6,0 6) *
0,7,0 7) *
scsibus1:
1,0,0 100) *
1,1,0 101) *
1,2,0 102) *
1,3,0 103) *
1,4,0 104) *
1,5,0 105) 'YAMAHA ' 'CRW4260 ' '1.0q' Removable CD-ROM
1,6,0 106) 'ARTEC ' 'AM12S ' '1.06' Scanner
1,7,0 107) *
Locate the entry for the CD burner and use the three numbers separated by commas as the value for dev. In this case, the Yamaha burner device is 1,5,0, so the appropriate input to specify that device is dev=1,5,0. Refer to the manual page for cdrecord for other ways to specify this value and for information on writing audio tracks and controlling the write speed.
Alternately, run the following command to get the device address of the burner:
# camcontrol devlist
<MATSHITA CDRW/DVD UJDA740 1.00> at scbus1 target 0 lun 0 (cd0,pass0)
Use the numeric values for scbus, target, and lun. For this example, 1,0,0 is the device name to use.
--------------
在FreeBSD中，cdrecord可用于刻录CD。该命令与sysutils/cdrtools软件包或端口一起安装。
虽然cdrecord有许多选项，但基本用法很简单。指定要刻录的ISO文件的名称，如果系统有多个燃烧器设备，则指定要使用的设备的名称：
#cdrecord dev=设备映像文件.iso
要确定燃烧器的设备名称，请使用-scanbus，它可能会产生如下结果：
#cdrecord-扫描总线
ProDVD ProBD Clone 3.00（amd64-unknown-freebsd10.0）版权所有（C）1995-2010 Jörg Schilling
使用libscg版本“schily-0.9”
scsibus0:
0,0,0 0）“SEAGATE”“ST39236LW”“0004”磁盘
0,1,0 1）“SEAGATE”“ST39173W”“5958”磁盘
0,2,0 2）*
0,3,0 3）“iomega”“jaz 1GB”“J.86”可移动磁盘
0,4,0 4）“NEC”CD-ROM驱动器：466“1.26”可移动CD-ROM
0,5,0 5）*
0,6,0 6）*
0,7,0 7）*
scsibus1：
1,0,0 100）*
1,1,0 101）*
1,2,0 102）*
1,3,0 103）*
1,4,0 104）*
1,5,0 105）“YAMAHA”“CRW4260”“1.0q”可移动CD-ROM
1,6,0 106）“ARTEC”“AM12S”“1.06”扫描仪
1,7,0 107）*
找到CD刻录机的条目，并使用以逗号分隔的三个数字作为dev.的值。在这种情况下，雅马哈刻录机设备为1,5,0，因此指定该设备的适当输入为dev=1,5,0。有关指定该值的其他方法，以及有关写入音频曲目和控制写入速度的信息，请参阅cdrecord的手册页。
或者，运行以下命令以获取燃烧器的设备地址：
#camcontrol开发列表
<MATSHITA CDRW/DVD UJDA740 1.00>位于scbus1目标0 lun 0（cd0，pass0）
对scbus、target和lun使用数值。对于此示例，1,0,0是要使用的设备名称。
While cdrecord has many options, basic usage is simple. Specify the name of the ISO file to burn and, if the system has multiple burner devices, specify the name of the device to use:
# cdrecord dev=device imagefile.iso
To determine the device name of the burner, use -scanbus which might produce results like this:
# cdrecord -scanbus
ProDVD-ProBD-Clone 3.00 (amd64-unknown-freebsd10.0) Copyright (C) 1995-2010 Jörg Schilling
Using libscg version 'schily-0.9'
scsibus0:
0,0,0 0) 'SEAGATE ' 'ST39236LW ' '0004' Disk
0,1,0 1) 'SEAGATE ' 'ST39173W ' '5958' Disk
0,2,0 2) *
0,3,0 3) 'iomega ' 'jaz 1GB ' 'J.86' Removable Disk
0,4,0 4) 'NEC ' 'CD-ROM DRIVE:466' '1.26' Removable CD-ROM
0,5,0 5) *
0,6,0 6) *
0,7,0 7) *
scsibus1:
1,0,0 100) *
1,1,0 101) *
1,2,0 102) *
1,3,0 103) *
1,4,0 104) *
1,5,0 105) 'YAMAHA ' 'CRW4260 ' '1.0q' Removable CD-ROM
1,6,0 106) 'ARTEC ' 'AM12S ' '1.06' Scanner
1,7,0 107) *
Locate the entry for the CD burner and use the three numbers separated by commas as the value for dev. In this case, the Yamaha burner device is 1,5,0, so the appropriate input to specify that device is dev=1,5,0. Refer to the manual page for cdrecord for other ways to specify this value and for information on writing audio tracks and controlling the write speed.
Alternately, run the following command to get the device address of the burner:
# camcontrol devlist
<MATSHITA CDRW/DVD UJDA740 1.00> at scbus1 target 0 lun 0 (cd0,pass0)
Use the numeric values for scbus, target, and lun. For this example, 1,0,0 is the device name to use.
--------------
在FreeBSD中，cdrecord可用于刻录CD。该命令与sysutils/cdrtools软件包或端口一起安装。
虽然cdrecord有许多选项，但基本用法很简单。指定要刻录的ISO文件的名称，如果系统有多个燃烧器设备，则指定要使用的设备的名称：
#cdrecord dev=设备映像文件.iso
要确定燃烧器的设备名称，请使用-scanbus，它可能会产生如下结果：
#cdrecord-扫描总线
ProDVD ProBD Clone 3.00（amd64-unknown-freebsd10.0）版权所有（C）1995-2010 Jörg Schilling
使用libscg版本“schily-0.9”
scsibus0:
0,0,0 0）“SEAGATE”“ST39236LW”“0004”磁盘
0,1,0 1）“SEAGATE”“ST39173W”“5958”磁盘
0,2,0 2）*
0,3,0 3）“iomega”“jaz 1GB”“J.86”可移动磁盘
0,4,0 4）“NEC”CD-ROM驱动器：466“1.26”可移动CD-ROM
0,5,0 5）*
0,6,0 6）*
0,7,0 7）*
scsibus1：
1,0,0 100）*
1,1,0 101）*
1,2,0 102）*
1,3,0 103）*
1,4,0 104）*
1,5,0 105）“YAMAHA”“CRW4260”“1.0q”可移动CD-ROM
1,6,0 106）“ARTEC”“AM12S”“1.06”扫描仪
1,7,0 107）*
找到CD刻录机的条目，并使用以逗号分隔的三个数字作为dev.的值。在这种情况下，雅马哈刻录机设备为1,5,0，因此指定该设备的适当输入为dev=1,5,0。有关指定该值的其他方法，以及有关写入音频曲目和控制写入速度的信息，请参阅cdrecord的手册页。
或者，运行以下命令以获取燃烧器的设备地址：
#camcontrol开发列表
<MATSHITA CDRW/DVD UJDA740 1.00>位于scbus1目标0 lun 0（cd0，pass0）
对scbus、target和lun使用数值。对于此示例，1,0,0是要使用的设备名称。
