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(itstool) path: sect1/para
English
A comprehensive permission delegation system allows unprivileged users to perform <acronym>ZFS</acronym> administration functions. For example, if each user's home directory is a dataset, users can be given permission to create and destroy snapshots of their home directories. A backup user can be given permission to use replication features. A usage statistics script can be allowed to run with access only to the space utilization data for all users. It is even possible to delegate the ability to delegate permissions. Permission delegation is possible for each subcommand and most properties.
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Context English Chinese (Simplified) (zh_CN) State
To activate deduplication, set the <literal>dedup</literal> property on the target pool: 要开启去重复功能，需在目标存储池设定 <literal>dedup</literal> 属性：
<prompt>#</prompt> <userinput>zfs set dedup=on <replaceable>pool</replaceable></userinput> <prompt>#</prompt> <userinput>zfs set dedup=on <replaceable>pool</replaceable></userinput>
Only new data being written to the pool will be deduplicated. Data that has already been written to the pool will not be deduplicated merely by activating this option. A pool with a freshly activated deduplication property will look like this example: 只有要被写入到存储池的新资料才会做去重复的动作，先前已被写入到存储池的资料不会因此启动了这个选项而做去重复。查看已开启去重复属性的存储池会如下：
<prompt>#</prompt> <userinput>zpool list</userinput>
NAME SIZE ALLOC FREE CKPOINT EXPANDSZ FRAG CAP DEDUP HEALTH ALTROOT
pool 2.84G 2.19M 2.83G - - 0% 0% 1.00x ONLINE - 		<prompt>#</prompt> <userinput>zpool list</userinput>
NAME SIZE ALLOC FREE CKPOINT EXPANDSZ FRAG CAP DEDUP HEALTH ALTROOT
pool 2.84G 2.19M 2.83G - - 0% 0% 1.00x ONLINE -
The <literal>DEDUP</literal> column shows the actual rate of deduplication for the pool. A value of <literal>1.00x</literal> shows that data has not been deduplicated yet. In the next example, the ports tree is copied three times into different directories on the deduplicated pool created above. <literal>DEDUP</literal> 栏位会显示存储池的实际去重复率，数值为 <literal>1.00x</literal> 代表资料尚未被去重复.在下一个例子会在前面所建立的去重复存储池中复制三份 Port 树到不同的目录中。
<prompt>#</prompt> <userinput>for d in dir1 dir2 dir3; do</userinput>
&gt; <userinput>mkdir $d &amp;&amp; cp -R /usr/ports $d &amp;</userinput>
&gt; <userinput>done</userinput> 		<prompt>#</prompt> <userinput>for d in dir1 dir2 dir3; do</userinput>
&gt; <userinput>mkdir $d &amp;&amp; cp -R /usr/ports $d &amp;</userinput>
&gt; <userinput>done</userinput>
Redundant data is detected and deduplicated: 已经侦测到重复的资料并做去重复：
<prompt>#</prompt> <userinput>zpool list</userinput>
NAME SIZE ALLOC FREE CKPOINT EXPANDSZ FRAG CAP DEDUP HEALTH ALTROOT
pool 2.84G 20.9M 2.82G - - 0% 0% 3.00x ONLINE - 		<prompt>#</prompt> <userinput>zpool list</userinput>
NAME SIZE ALLOC FREE CKPOINT EXPANDSZ FRAG CAP DEDUP HEALTH ALTROOT
pool 2.84G 20.9M 2.82G - - 0% 0% 3.00x ONLINE -
The <literal>DEDUP</literal> column shows a factor of <literal>3.00x</literal>. Multiple copies of the ports tree data was detected and deduplicated, using only a third of the space. The potential for space savings can be enormous, but comes at the cost of having enough memory to keep track of the deduplicated blocks. <literal>DEDUP</literal> 栏位显示有<literal>3.00x</literal> 的去重复率，这代表已侦测到多份复制的Port 树资料并做了去重复的动作，且只会使用第三份资料所占的空间.去重复能节省空间的潜力可以非常巨大，但会需要消耗大量的内存来持续追踪去重复的资料区块。
Deduplication is not always beneficial, especially when the data on a pool is not redundant. <acronym>ZFS</acronym> can show potential space savings by simulating deduplication on an existing pool: 去重复并非总是有效益的，特别是当存储池中的资料本身并没有重复时。 <acronym>ZFS</acronym> 可以透过在现有存储池上模拟开启去重复功能来显示可能节省的空间：
<prompt>#</prompt> <userinput>zdb -S <replaceable>pool</replaceable></userinput>
Simulated DDT histogram:

bucket allocated referenced
______ ______________________________ ______________________________
refcnt blocks LSIZE PSIZE DSIZE blocks LSIZE PSIZE DSIZE
------ ------ ----- ----- ----- ------ ----- ----- -----
1 2.58M 289G 264G 264G 2.58M 289G 264G 264G
2 206K 12.6G 10.4G 10.4G 430K 26.4G 21.6G 21.6G
4 37.6K 692M 276M 276M 170K 3.04G 1.26G 1.26G
8 2.18K 45.2M 19.4M 19.4M 20.0K 425M 176M 176M
16 174 2.83M 1.20M 1.20M 3.33K 48.4M 20.4M 20.4M
32 40 2.17M 222K 222K 1.70K 97.2M 9.91M 9.91M
64 9 56K 10.5K 10.5K 865 4.96M 948K 948K
128 2 9.50K 2K 2K 419 2.11M 438K 438K
256 5 61.5K 12K 12K 1.90K 23.0M 4.47M 4.47M
1K 2 1K 1K 1K 2.98K 1.49M 1.49M 1.49M
Total 2.82M 303G 275G 275G 3.20M 319G 287G 287G

dedup = 1.05, compress = 1.11, copies = 1.00, dedup * compress / copies = 1.16 		<prompt>#</prompt> <userinput>zdb -S <replaceable>pool</replaceable></userinput>
Simulated DDT histogram:

bucket allocated referenced
______ ______________________________ ______________________________
refcnt blocks LSIZE PSIZE DSIZE blocks LSIZE PSIZE DSIZE
------ ------ ----- ----- ----- ------ ----- ----- -----
1 2.58M 289G 264G 264G 2.58M 289G 264G 264G
2 206K 12.6G 10.4G 10.4G 430K 26.4G 21.6G 21.6G
4 37.6K 692M 276M 276M 170K 3.04G 1.26G 1.26G
8 2.18K 45.2M 19.4M 19.4M 20.0K 425M 176M 176M
16 174 2.83M 1.20M 1.20M 3.33K 48.4M 20.4M 20.4M
32 40 2.17M 222K 222K 1.70K 97.2M 9.91M 9.91M
64 9 56K 10.5K 10.5K 865 4.96M 948K 948K
128 2 9.50K 2K 2K 419 2.11M 438K 438K
256 5 61.5K 12K 12K 1.90K 23.0M 4.47M 4.47M
1K 2 1K 1K 1K 2.98K 1.49M 1.49M 1.49M
Total 2.82M 303G 275G 275G 3.20M 319G 287G 287G

dedup = 1.05, compress = 1.11, copies = 1.00, dedup * compress / copies = 1.16
After <command>zdb -S</command> finishes analyzing the pool, it shows the space reduction ratio that would be achieved by activating deduplication. In this case, <literal>1.16</literal> is a very poor space saving ratio that is mostly provided by compression. Activating deduplication on this pool would not save any significant amount of space, and is not worth the amount of memory required to enable deduplication. Using the formula <emphasis>ratio = dedup * compress / copies</emphasis>, system administrators can plan the storage allocation, deciding whether the workload will contain enough duplicate blocks to justify the memory requirements. If the data is reasonably compressible, the space savings may be very good. Enabling compression first is recommended, and compression can also provide greatly increased performance. Only enable deduplication in cases where the additional savings will be considerable and there is sufficient memory for the <link linkend="zfs-term-deduplication"><acronym>DDT</acronym></link>. 在 <command>zdb -S</command> 分析完存储池后会显示在启动去重复后可达到的空间减少比例。在本例中，<literal>1。16</literal> 是非常差的空间节省比例，因为这个比例使用压缩功能便能达成。若在此存储池上启动去重复并不能明显的节省空间使用量，那么就不值得耗费大量的内存来开启去重复功能。透过公式 <emphasis>ratio = dedup * compress / copies</emphasis>，系统管理者可以规划储存空间的配置，来判断要处理的资料是否有足够的重复资料区块来平衡所需的内存。若资料是可压缩的，那么空间节少的效果可能会非常好，建议先开启压缩功能，且压缩功能也可以大大提高效能。去重复功能只有在可以节省可观的空间且有足够的内存做 <link linkend="zfs-term-deduplication"><acronym>DDT</acronym></link> 时才开启。
<acronym>ZFS</acronym> and Jails <acronym>ZFS</acronym> 与Jail
<command>zfs jail</command> and the corresponding <literal>jailed</literal> property are used to delegate a <acronym>ZFS</acronym> dataset to a <link linkend="jails">Jail</link>. <command>zfs jail <replaceable>jailid</replaceable></command> attaches a dataset to the specified jail, and <command>zfs unjail</command> detaches it. For the dataset to be controlled from within a jail, the <literal>jailed</literal> property must be set. Once a dataset is jailed, it can no longer be mounted on the host because it may have mount points that would compromise the security of the host. <command>zfs jail</command> 以及相关的<literal>jailed</literal> 属性可以用来将一个<acronym>ZFS</acronym> 数据集委托给一个 <link linkend="jails">Jail</link> 管理。<command>zfs jail <replaceable>jailid</replaceable></command> 可以将一个数据集连结到一个指定的 Jail，而 <command>zfs unjail</command> 则可解除连结。数据集要可以在 Jail 中控制需设定 <literal>jailed</literal> 属性，一旦数据集被隔离便无法再挂载到主机，因为有挂载点可能会破坏主机的安全性。
Delegated Administration 委托管理
A comprehensive permission delegation system allows unprivileged users to perform <acronym>ZFS</acronym> administration functions. For example, if each user's home directory is a dataset, users can be given permission to create and destroy snapshots of their home directories. A backup user can be given permission to use replication features. A usage statistics script can be allowed to run with access only to the space utilization data for all users. It is even possible to delegate the ability to delegate permissions. Permission delegation is possible for each subcommand and most properties. 一个全面性的权限委托系统可能无权限的使用者执行 <acronym>ZFS</acronym> 的管理功能。例如，若每个使用者的家目录均为一个数据集，便可以给予使用者权限建立与摧毁它们家目录中的快照。可以给予备份使用者使用备份功能的权限。一个使用量统计的 Script 可以允许其在执行时能存取所有使用者的空间利用率资料。甚至可以将委托权限委托给其他人，每个子指令与大多数属性都可使用权限委托。
Delegating Dataset Creation 委托数据集建立
<command>zfs allow <replaceable>someuser</replaceable> create <replaceable>mydataset</replaceable></command> gives the specified user permission to create child datasets under the selected parent dataset. There is a caveat: creating a new dataset involves mounting it. That requires setting the FreeBSD <literal>vfs.usermount</literal> <citerefentry><refentrytitle>sysctl</refentrytitle><manvolnum>8</manvolnum></citerefentry> to <literal>1</literal> to allow non-root users to mount a file system. There is another restriction aimed at preventing abuse: non-<systemitem class="username">root</systemitem> users must own the mountpoint where the file system is to be mounted. <command>zfs allow <replaceable>someuser</replaceable> create <replaceable>mydataset</replaceable></command> 可以给予指定的使用者在指定的父数据集下建立子数据集的权限。这里需要注意：建立新数据集会牵涉到挂载，因此需要设定 FreeBSD 的<literal>vfs.usermount</literal> <citerefentry><refentrytitle>sysctl</refentrytitle><manvolnum>8</manvolnum></citerefentry > 为<literal>1</literal> 来允许非root 的使用者挂载一个文件系统。这里还有另一项限制可以避免滥用：非 <systemitem class="username">root</systemitem> 使用者必须拥有挂载点在文件系统中所在位置的权限才可挂载。
Delegating Permission Delegation 委托权限委托
<command>zfs allow <replaceable>someuser</replaceable> allow <replaceable>mydataset</replaceable></command> gives the specified user the ability to assign any permission they have on the target dataset, or its children, to other users. If a user has the <literal>snapshot</literal> permission and the <literal>allow</literal> permission, that user can then grant the <literal>snapshot</literal> permission to other users. <command>zfs allow <replaceable>someuser</replaceable> allow <replaceable>mydataset</replaceable></command> 可以给予指定的使用者有权限指派它们在目标数据集或其子数据集上拥有的任何权限给其他人。若该使用者拥有 <literal>snapshot</literal> 权限及 <literal>allow</literal> 权限，则该使用者可以授权 <literal>snapshot</literal> 权限给其他使用者。
Tuning 优化调整
There are a number of tunables that can be adjusted to make <acronym>ZFS</acronym> perform best for different workloads. 这里有数个可调校的项目可以调整，来让 <acronym>ZFS</acronym> 在面对各种工作都能以最佳状况运作。
<emphasis><varname>vfs.zfs.arc_max</varname></emphasis> - Maximum size of the <link linkend="zfs-term-arc"><acronym>ARC</acronym></link>. The default is all <acronym>RAM</acronym> but 1 GB, or 5/8 of all <acronym>RAM</acronym>, whichever is more. However, a lower value should be used if the system will be running any other daemons or processes that may require memory. This value can be adjusted at runtime with <citerefentry><refentrytitle>sysctl</refentrytitle><manvolnum>8</manvolnum></citerefentry> and can be set in <filename>/boot/loader.conf</filename> or <filename>/etc/sysctl.conf</filename>. <emphasis><varname>vfs.zfs.arc_max</varname></emphasis> - <link linkend="zfs-term-arc"><acronym>ARC</acronym></link>最大容量。默认为全部RAM。如果有运行其他程序，此处应设置一个较低的值可在系统运行时使用<citerefentry><refentrytitle>sysctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>调整，也可在 <filename>/boot/loader.conf</filename> 或 <filename>/etc/sysctl.conf</filename>中进行设置（需重启系统）。
<emphasis><varname>vfs.zfs.arc_meta_limit</varname></emphasis> - Limit the portion of the <link linkend="zfs-term-arc"><acronym>ARC</acronym></link> that can be used to store metadata. The default is one fourth of <varname>vfs.zfs.arc_max</varname>. Increasing this value will improve performance if the workload involves operations on a large number of files and directories, or frequent metadata operations, at the cost of less file data fitting in the <link linkend="zfs-term-arc"><acronym>ARC</acronym></link>. This value can be adjusted at runtime with <citerefentry><refentrytitle>sysctl</refentrytitle><manvolnum>8</manvolnum></citerefentry> and can be set in <filename>/boot/loader.conf</filename> or <filename>/etc/sysctl.conf</filename>. <emphasis><varname>vfs.zfs.arc_meta_limit</varname></emphasis> - 限制 <link linkend="zfs-term-arc"><acronym>ARC</acronym></link> 中可用于存储元数据的部分。默认值是 <varname>vfs.zfs.arc_max</varname> 的四分之一。如果工作负载涉及到对大量文件和目录的修改，或频繁地修改元数据，那么增加该值将提高性能，但代价是减少 <link linkend="zfs-term-arc"><acronym>ARC</acronym></link> 中的文件数据拟合。该值可以使用 <citerefentry><refentrytitle>sysctl</refentrytitle><manvolnum>8</manvolnum></citerefentry> 调整，可以以在 <filename>/boot/loader.conf</filename> 或 <filename>/etc/sysctl.conf</filename> 中设置。
<emphasis><varname>vfs.zfs.arc_min</varname></emphasis> - Minimum size of the <link linkend="zfs-term-arc"><acronym>ARC</acronym></link>. The default is one half of <varname>vfs.zfs.arc_meta_limit</varname>. Adjust this value to prevent other applications from pressuring out the entire <link linkend="zfs-term-arc"><acronym>ARC</acronym></link>. This value can be adjusted at runtime with <citerefentry><refentrytitle>sysctl</refentrytitle><manvolnum>8</manvolnum></citerefentry> and can be set in <filename>/boot/loader.conf</filename> or <filename>/etc/sysctl.conf</filename>. <emphasis><varname>vfs.zfs.arc_min</varname></emphasis> - <link linkend="zfs-term-arc"><acronym>ARC</acronym></link>的最小尺寸。默认值是<varname>vfs.zfs.arc_meta_limit</varname>的一半。调整该值以防止其他应用程序压出整个 <link linkend="zfs-term-arc"><acronym>ARC</acronym></link>。这个值可以在运行时用<citerefentry><refentrytitle>sysctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>来调整，并且可以在<filename>/boot/loader.conf</filename>或<filename>/etc/sysctl.conf</filename>中设置。
<emphasis><varname>vfs.zfs.vdev.cache.size</varname></emphasis> - A preallocated amount of memory reserved as a cache for each device in the pool. The total amount of memory used will be this value multiplied by the number of devices. This value can only be adjusted at boot time, and is set in <filename>/boot/loader.conf</filename>. <emphasis><varname>vfs.zfs.vdev.cache.size</varname></emphasis> - 预先分配的内存量，作为池中每个设备的缓存。使用的内存总量将是这个值乘以设备数量。此值只能在操作系统启动时调整，可以在 <filename>/boot/loader.conf</filename>中设置。
<emphasis><varname>vfs.zfs.min_auto_ashift</varname></emphasis> - Minimum <varname>ashift</varname> (sector size) that will be used automatically at pool creation time. The value is a power of two. The default value of <literal>9</literal> represents <literal>2^9 = 512</literal>, a sector size of 512 bytes. To avoid <emphasis>write amplification</emphasis> and get the best performance, set this value to the largest sector size used by a device in the pool. <emphasis><varname>vfs.zfs.min_auto_ashift</varname></emphasis> - 在创建池时自动使用的最小<varname>ashift</varname>（扇区大小）。该值是二的幂。默认值<literal>9</literal>表示<literal>2^9 = 512</literal>，扇区大小为512字节。为了避免<emphasis>写放大</emphasis>并获得最佳性能，请将此值设置为池中设备使用的最大扇区大小。
Many drives have 4 KB sectors. Using the default <varname>ashift</varname> of <literal>9</literal> with these drives results in write amplification on these devices. Data that could be contained in a single 4 KB write must instead be written in eight 512-byte writes. <acronym>ZFS</acronym> tries to read the native sector size from all devices when creating a pool, but many drives with 4 KB sectors report that their sectors are 512 bytes for compatibility. Setting <varname>vfs.zfs.min_auto_ashift</varname> to <literal>12</literal> (<literal>2^12 = 4096</literal>) before creating a pool forces <acronym>ZFS</acronym> to use 4 KB blocks for best performance on these drives. 许多驱动器有4KB的扇区。在这些硬盘上使用默认的<varname>ashift</varname><literal>9</literal>，会导致这些设备上的写入量放大。原本可以包含在单个 4 KB 写入中的数据必须以 8 个 512 字节的写入方式写入。<acronym>ZFS</acronym>在创建池时，会尝试从所有设备中读取本机扇区大小，但许多具有4 KB扇区的驱动器报告说，为了兼容性，它们的扇区是512字节。在创建池之前，将 <varname>vfs.zfs.min_auto_ashift</varname>设置为 <literal>12</literal> (<literal>2^12 = 4096</literal>)，可迫使 <acronym>ZFS</acronym>使用 4 KB 块，以获得这些驱动器上的最佳性能。
Forcing 4 KB blocks is also useful on pools where disk upgrades are planned. Future disks are likely to use 4 KB sectors, and <varname>ashift</varname> values cannot be changed after a pool is created. 强制使用 4KB 块在计划进行磁盘升级的池中也很有用。将来的磁盘可能会使用 4 KB 扇区，并且在创建池后无法更改<varname>ashift</varname>值。
In some specific cases, the smaller 512-byte block size might be preferable. When used with 512-byte disks for databases, or as storage for virtual machines, less data is transferred during small random reads. This can provide better performance, especially when using a smaller <acronym>ZFS</acronym> record size. 在某些特定情况下，使用较小的 512 字节块大小可能更合适。当与 512 字节的数据库磁盘一起使用时，或用作虚拟机的存储时，在小型随机读取期间传输的数据较少。这可以提供更好的性能，尤其是在使用较小的<acronym>ZFS</acronym>记录大小时。
<emphasis><varname>vfs.zfs.prefetch_disable</varname></emphasis> - Disable prefetch. A value of <literal>0</literal> is enabled and <literal>1</literal> is disabled. The default is <literal>0</literal>, unless the system has less than 4 GB of <acronym>RAM</acronym>. Prefetch works by reading larger blocks than were requested into the <link linkend="zfs-term-arc"><acronym>ARC</acronym></link> in hopes that the data will be needed soon. If the workload has a large number of random reads, disabling prefetch may actually improve performance by reducing unnecessary reads. This value can be adjusted at any time with <citerefentry><refentrytitle>sysctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>. <emphasis><varname>vfs.zfs.prefetch_disable</varname></emphasis> - 禁用预取。<literal>0</literal>为启用，<literal>1</literal>为禁用。默认值是<literal>0</literal>，除非系统的<acronym>RAM</acronym>小于4 GB。预取的工作方式是向 <link linkend="zfs-term-arc"><acronym>ARC</acronym></link>中读取比请求的数据块更大的数据块，希望很快就会需要这些数据。如果工作负载有大量的随机读取，禁用预取实际上可以通过减少不必要的读取来提高性能。这个值可以随时用<citerefentry><refentrytitle>sysctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>调整。

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(itstool) path: sect1/para
Source string location
book.translate.xml:42446
String age
a year ago
Source string age
a year ago
Translation file
books/zh_CN/handbook.po, string 6966