Date: Wed, 14 Aug 2013 22:21:15 +0000 (UTC) From: Warren Block <wblock@FreeBSD.org> To: doc-committers@freebsd.org, svn-doc-projects@freebsd.org Subject: svn commit: r42540 - in projects/zfsupdate-201307/en_US.ISO8859-1/books/handbook: . bsdinstall filesystems zfs Message-ID: <201308142221.r7EMLF8w074299@svn.freebsd.org>
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Author: wblock Date: Wed Aug 14 22:21:15 2013 New Revision: 42540 URL: http://svnweb.freebsd.org/changeset/doc/42540 Log: Split the ZFS content into a separate chapter. Added: projects/zfsupdate-201307/en_US.ISO8859-1/books/handbook/zfs/ projects/zfsupdate-201307/en_US.ISO8859-1/books/handbook/zfs/chapter.xml - copied, changed from r42538, projects/zfsupdate-201307/en_US.ISO8859-1/books/handbook/filesystems/chapter.xml Modified: projects/zfsupdate-201307/en_US.ISO8859-1/books/handbook/Makefile projects/zfsupdate-201307/en_US.ISO8859-1/books/handbook/book.xml projects/zfsupdate-201307/en_US.ISO8859-1/books/handbook/bsdinstall/chapter.xml projects/zfsupdate-201307/en_US.ISO8859-1/books/handbook/chapters.ent projects/zfsupdate-201307/en_US.ISO8859-1/books/handbook/filesystems/chapter.xml Modified: projects/zfsupdate-201307/en_US.ISO8859-1/books/handbook/Makefile ============================================================================== --- projects/zfsupdate-201307/en_US.ISO8859-1/books/handbook/Makefile Wed Aug 14 21:50:46 2013 (r42539) +++ projects/zfsupdate-201307/en_US.ISO8859-1/books/handbook/Makefile Wed Aug 14 22:21:15 2013 (r42540) @@ -278,6 +278,7 @@ SRCS+= serialcomms/chapter.xml SRCS+= users/chapter.xml SRCS+= virtualization/chapter.xml SRCS+= x11/chapter.xml +SRCS+= zfs/chapter.xml # Entities SRCS+= chapters.ent Modified: projects/zfsupdate-201307/en_US.ISO8859-1/books/handbook/book.xml ============================================================================== --- projects/zfsupdate-201307/en_US.ISO8859-1/books/handbook/book.xml Wed Aug 14 21:50:46 2013 (r42539) +++ projects/zfsupdate-201307/en_US.ISO8859-1/books/handbook/book.xml Wed Aug 14 22:21:15 2013 (r42540) @@ -235,6 +235,7 @@ &chap.audit; &chap.disks; &chap.geom; + &chap.zfs; &chap.filesystems; &chap.virtualization; &chap.l10n; Modified: projects/zfsupdate-201307/en_US.ISO8859-1/books/handbook/bsdinstall/chapter.xml ============================================================================== --- projects/zfsupdate-201307/en_US.ISO8859-1/books/handbook/bsdinstall/chapter.xml Wed Aug 14 21:50:46 2013 (r42539) +++ projects/zfsupdate-201307/en_US.ISO8859-1/books/handbook/bsdinstall/chapter.xml Wed Aug 14 22:21:15 2013 (r42540) @@ -1411,7 +1411,7 @@ Trying to mount root from cd9660:/dev/is <para>Another partition type worth noting is <literal>freebsd-zfs</literal>, used for partitions that will contain a &os; ZFS filesystem. See - <xref linkend="filesystems-zfs"/>. &man.gpart.8; shows more + <xref linkend="zfs"/>. &man.gpart.8; shows more of the available <acronym>GPT</acronym> partition types.</para> Modified: projects/zfsupdate-201307/en_US.ISO8859-1/books/handbook/chapters.ent ============================================================================== --- projects/zfsupdate-201307/en_US.ISO8859-1/books/handbook/chapters.ent Wed Aug 14 21:50:46 2013 (r42539) +++ projects/zfsupdate-201307/en_US.ISO8859-1/books/handbook/chapters.ent Wed Aug 14 22:21:15 2013 (r42540) @@ -38,6 +38,7 @@ <!ENTITY chap.audit SYSTEM "audit/chapter.xml"> <!ENTITY chap.disks SYSTEM "disks/chapter.xml"> <!ENTITY chap.geom SYSTEM "geom/chapter.xml"> + <!ENTITY chap.zfs SYSTEM "zfs/chapter.xml"> <!ENTITY chap.filesystems SYSTEM "filesystems/chapter.xml"> <!ENTITY chap.virtualization SYSTEM "virtualization/chapter.xml"> <!ENTITY chap.l10n SYSTEM "l10n/chapter.xml"> Modified: projects/zfsupdate-201307/en_US.ISO8859-1/books/handbook/filesystems/chapter.xml ============================================================================== --- projects/zfsupdate-201307/en_US.ISO8859-1/books/handbook/filesystems/chapter.xml Wed Aug 14 21:50:46 2013 (r42539) +++ projects/zfsupdate-201307/en_US.ISO8859-1/books/handbook/filesystems/chapter.xml Wed Aug 14 22:21:15 2013 (r42540) @@ -34,7 +34,7 @@ <acronym>UFS</acronym> which has been modernized as <acronym>UFS2</acronym>. Since &os; 7.0, the Z File System <acronym>ZFS</acronym> is also available as a native file - system.</para> + system. See <xref linkend="zfs"/> for more information.</para> <para>In addition to its native file systems, &os; supports a multitude of other file systems so that data from other @@ -96,1439 +96,6 @@ </itemizedlist> </sect1> - <sect1 id="filesystems-zfs"> - <title>The Z File System (ZFS)</title> - - <para>The Z file system, originally developed by &sun;, - is designed to future proof the file system by removing many of - the arbitrary limits imposed on previous file systems. ZFS - allows continuous growth of the pooled storage by adding - additional devices. ZFS allows you to create many file systems - (in addition to block devices) out of a single shared pool of - storage. Space is allocated as needed, so all remaining free - space is available to each file system in the pool. It is also - designed for maximum data integrity, supporting data snapshots, - multiple copies, and cryptographic checksums. It uses a - software data replication model, known as - <acronym>RAID</acronym>-Z. <acronym>RAID</acronym>-Z provides - redundancy similar to hardware <acronym>RAID</acronym>, but is - designed to prevent data write corruption and to overcome some - of the limitations of hardware <acronym>RAID</acronym>.</para> - - <sect2 id="filesystems-zfs-term"> - <title>ZFS Features and Terminology</title> - - <para>ZFS is a fundamentally different file system because it - is more than just a file system. ZFS combines the roles of - file system and volume manager, enabling additional storage - devices to be added to a live system and having the new space - available on all of the existing file systems in that pool - immediately. By combining the traditionally separate roles, - ZFS is able to overcome previous limitations that prevented - RAID groups being able to grow. Each top level device in a - zpool is called a vdev, which can be a simple disk or a RAID - transformation such as a mirror or RAID-Z array. ZFS file - systems (called datasets), each have access to the combined - free space of the entire pool. As blocks are allocated the - free space in the pool available to of each file system is - decreased. This approach avoids the common pitfall with - extensive partitioning where free space becomes fragmentated - across the partitions.</para> - - <informaltable pgwide="1"> - <tgroup cols="2"> - <tbody> - <row> - <entry valign="top" - id="filesystems-zfs-term-zpool">zpool</entry> - - <entry>A storage pool is the most basic building block - of ZFS. A pool is made up of one or more vdevs, the - underlying devices that store the data. A pool is - then used to create one or more file systems - (datasets) or block devices (volumes). These datasets - and volumes share the pool of remaining free space. - Each pool is uniquely identified by a name and a - <acronym>GUID</acronym>. The zpool also controls the - version number and therefore the features available - for use with ZFS. - <note><para>&os; 9.0 and 9.1 include - support for ZFS version 28. Future versions use ZFS - version 5000 with feature flags. This allows - greater cross-compatibility with other - implementations of ZFS. - </para></note></entry> - </row> - - <row> - <entry valign="top" - id="filesystems-zfs-term-vdev">vdev Types</entry> - - <entry>A zpool is made up of one or more vdevs, which - themselves can be a single disk or a group of disks, - in the case of a RAID transform. When multiple vdevs - are used, ZFS spreads data across the vdevs to - increase performance and maximize usable space. - <itemizedlist> - <listitem> - <para id="filesystems-zfs-term-vdev-disk"> - <emphasis>Disk</emphasis> - The most basic type - of vdev is a standard block device. This can be - an entire disk (such as - <devicename><replaceable>/dev/ada0</replaceable></devicename> - or - <devicename><replaceable>/dev/da0</replaceable></devicename>) - or a partition - (<devicename><replaceable>/dev/ada0p3</replaceable></devicename>). - Contrary to the Solaris documentation, on &os; - there is no performance penalty for using a - partition rather than an entire disk.</para> - </listitem> - - <listitem> - <para id="filesystems-zfs-term-vdev-file"> - <emphasis>File</emphasis> - In addition to - disks, ZFS pools can be backed by regular files, - this is especially useful for testing and - experimentation. Use the full path to the file - as the device path in the zpool create command. - All vdevs must be atleast 128 MB in - size.</para> - </listitem> - - <listitem> - <para id="filesystems-zfs-term-vdev-mirror"> - <emphasis>Mirror</emphasis> - When creating a - mirror, specify the <literal>mirror</literal> - keyword followed by the list of member devices - for the mirror. A mirror consists of two or - more devices, all data will be written to all - member devices. A mirror vdev will only hold as - much data as its smallest member. A mirror vdev - can withstand the failure of all but one of its - members without losing any data.</para> - - <note> - <para> - A regular single disk vdev can be - upgraded to a mirror vdev at any time using - the <command>zpool</command> <link - linkend="filesystems-zfs-zpool-attach">attach</link> - command.</para> - </note> - </listitem> - - <listitem> - <para id="filesystems-zfs-term-vdev-raidz"> - <emphasis><acronym>RAID</acronym>-Z</emphasis> - - ZFS implements RAID-Z, a variation on standard - RAID-5 that offers better distribution of parity - and eliminates the "RAID-5 write hole" in which - the data and parity information become - inconsistent after an unexpected restart. ZFS - supports 3 levels of RAID-Z which provide - varying levels of redundancy in exchange for - decreasing levels of usable storage. The types - are named RAID-Z1 through Z3 based on the number - of parity devinces in the array and the number - of disks that the pool can operate - without.</para> - - <para>In a RAID-Z1 configuration with 4 disks, - each 1 TB, usable storage will be 3 TB - and the pool will still be able to operate in - degraded mode with one faulted disk. If an - additional disk goes offline before the faulted - disk is replaced and resilvered, all data in the - pool can be lost.</para> - - <para>In a RAID-Z3 configuration with 8 disks of - 1 TB, the volume would provide 5TB of - usable space and still be able to operate with - three faulted disks. Sun recommends no more - than 9 disks in a single vdev. If the - configuration has more disks, it is recommended - to divide them into separate vdevs and the pool - data will be striped across them.</para> - - <para>A configuration of 2 RAID-Z2 vdevs - consisting of 8 disks each would create - something similar to a RAID 60 array. A RAID-Z - group's storage capacity is approximately the - size of the smallest disk, multiplied by the - number of non-parity disks. 4x 1 TB disks - in Z1 has an effective size of approximately - 3 TB, and a 8x 1 TB array in Z3 will - yeild 5 TB of usable space.</para> - </listitem> - - <listitem> - <para id="filesystems-zfs-term-vdev-spare"> - <emphasis>Spare</emphasis> - ZFS has a special - pseudo-vdev type for keeping track of available - hot spares. Note that installed hot spares are - not deployed automatically; they must manually - be configured to replace the failed device using - the zfs replace command.</para> - </listitem> - - <listitem> - <para id="filesystems-zfs-term-vdev-log"> - <emphasis>Log</emphasis> - ZFS Log Devices, also - known as ZFS Intent Log (<acronym>ZIL</acronym>) - move the intent log from the regular pool - devices to a dedicated device. The ZIL - accelerates synchronous transactions by using - storage devices (such as - <acronym>SSD</acronym>s) that are faster - compared to those used for the main pool. When - data is being written and the application - requests a guarantee that the data has been - safely stored, the data is written to the faster - ZIL storage, then later flushed out to the - regular disks, greatly reducing the latency of - synchronous writes. Log devices can be - mirrored, but RAID-Z is not supported. When - specifying multiple log devices writes will be - load balanced across all devices.</para> - </listitem> - - <listitem> - <para id="filesystems-zfs-term-vdev-cache"> - <emphasis>Cache</emphasis> - Adding a cache vdev - to a zpool will add the storage of the cache to - the L2ARC. Cache devices cannot be mirrored. - Since a cache device only stores additional - copies of existing data, there is no risk of - data loss.</para> - </listitem> - </itemizedlist></entry> - </row> - - <row> - <entry valign="top" - id="filesystems-zfs-term-arc">Adaptive Replacement - Cache (<acronym>ARC</acronym>)</entry> - - <entry>ZFS uses an Adaptive Replacement Cache - (<acronym>ARC</acronym>), rather than a more - traditional Least Recently Used - (<acronym>LRU</acronym>) cache. An - <acronym>LRU</acronym> cache is a simple list of items - in the cache sorted by when each object was most - recently used; new items are added to the top of the - list and once the cache is full items from the bottom - of the list are evicted to make room for more active - objects. An <acronym>ARC</acronym> consists of four - lists; the Most Recently Used (<acronym>MRU</acronym>) - and Most Frequently Used (<acronym>MFU</acronym>) - objects, plus a ghost list for each. These ghost - lists tracks recently evicted objects to provent them - being added back to the cache. This increases the - cache hit ratio by avoiding objects that have a - history of only being used occasionally. Another - advantage of using both an <acronym>MRU</acronym> and - <acronym>MFU</acronym> is that scanning an entire - filesystem would normally evict all data from an - <acronym>MRU</acronym> or <acronym>LRU</acronym> cache - in favor of this freshly accessed content. In the - case of <acronym>ZFS</acronym> since there is also an - <acronym>MFU</acronym> that only tracks the most - frequently used objects, the cache of the most - commonly accessed blocks remains.</entry> - </row> - - <row> - <entry valign="top" - id="filesystems-zfs-term-l2arc">L2ARC</entry> - - <entry>The <acronym>L2ARC</acronym> is the second level - of the <acronym>ZFS</acronym> caching system. The - primary <acronym>ARC</acronym> is stored in - <acronym>RAM</acronym>, however since the amount of - available <acronym>RAM</acronym> is often limited, - <acronym>ZFS</acronym> can also make use of <link - linkend="filesystems-zfs-term-vdev-cache">cache</link> - vdevs. Solid State Disks (<acronym>SSD</acronym>s) - are often used as these cache devices due to their - higher speed and lower latency compared to traditional - spinning disks. An L2ARC is entirely optional, but - having one will significantly increase read speeds for - files that are cached on the <acronym>SSD</acronym> - instead of having to be read from the regular spinning - disks. The L2ARC can also speed up <link - linkend="filesystems-zfs-term-deduplication">deduplication</link> - since a <acronym>DDT</acronym> that does not fit in - <acronym>RAM</acronym> but does fit in the - <acronym>L2ARC</acronym> will be much faster than if - the <acronym>DDT</acronym> had to be read from disk. - The rate at which data is added to the cache devices - is limited to prevent prematurely wearing out the - <acronym>SSD</acronym> with too many writes. Until - the cache is full (the first block has been evicted to - make room), writing to the <acronym>L2ARC</acronym> is - limited to the sum of the write limit and the boost - limit, then after that limited to the write limit. A - pair of sysctl values control these rate limits; - <literal>vfs.zfs.l2arc_write_max</literal> controls - how many bytes are written to the cache per second, - while <literal>vfs.zfs.l2arc_write_boost</literal> - adds to this limit during the "Turbo Warmup Phase" - (Write Boost).</entry> - </row> - - <row> - <entry valign="top" - id="filesystems-zfs-term-cow">Copy-On-Write</entry> - - <entry>Unlike a traditional file system, when data is - overwritten on ZFS the new data is written to a - different block rather than overwriting the old data - in place. Only once this write is complete is the - metadata then updated to point to the new location of - the data. This means that in the event of a shorn - write (a system crash or power loss in the middle of - writing a file) the entire original contents of the - file are still available and the incomplete write is - discarded. This also means that ZFS does not require - a fsck after an unexpected shutdown.</entry> - </row> - - <row> - <entry valign="top" - id="filesystems-zfs-term-dataset">Dataset</entry> - - <entry>Dataset is the generic term for a ZFS file - system, volume, snapshot or clone. Each dataset will - have a unique name in the format: - <literal>poolname/path@snapshot</literal>. The root - of the pool is technically a dataset as well. Child - datasets are named hierarchically like directories; - for example <literal>mypool/home</literal>, the home - dataset is a child of mypool and inherits properties - from it. This can be expended further by creating - <literal>mypool/home/user</literal>. This grandchild - dataset will inherity properties from the parent and - grandparent. It is also possible to set properties - on a child to override the defaults inherited from the - parents and grandparents. ZFS also allows - administration of datasets and their children to be - delegated.</entry> - </row> - - <row> - <entry valign="top" - id="filesystems-zfs-term-volum">Volume</entry> - - <entry>In additional to regular file system datasets, - ZFS can also create volumes, which are block devices. - Volumes have many of the same features, including - copy-on-write, snapshots, clones and - checksumming. Volumes can be useful for running other - file system formats on top of ZFS, such as UFS or in - the case of Virtualization or exporting - <acronym>iSCSI</acronym> extents.</entry> - </row> - - <row> - <entry valign="top" - id="filesystems-zfs-term-snapshot">Snapshot</entry> - - <entry>The <link - linkend="filesystems-zfs-term-cow">copy-on-write</link> - design of ZFS allows for nearly instantaneous - consistent snapshots with arbitrary names. After - taking a snapshot of a dataset (or a recursive - snapshot of a parent dataset that will include all - child datasets), new data is written to new blocks (as - described above), however the old blocks are not - reclaimed as free space. There are then two versions - of the file system, the snapshot (what the file system - looked like before) and the live file system; however - no additional space is used. As new data is written - to the live file system, new blocks are allocated to - store this data. The apparent size of the snapshot - will grow as the blocks are no longer used in the live - file system, but only in the snapshot. These - snapshots can be mounted (read only) to allow for the - recovery of previous versions of files. It is also - possible to <link - linkend="filesystems-zfs-zfs-snapshot">rollback</link> - a live file system to a specific snapshot, undoing any - changes that took place after the snapshot was taken. - Each block in the zpool has a reference counter which - indicates how many snapshots, clones, datasets or - volumes make use of that block. As files and - snapshots are deleted, the reference count is - decremented; once a block is no longer referenced, it - is reclaimed as free space. Snapshots can also be - marked with a <link - linkend="filesystems-zfs-zfs-snapshot">hold</link>, - once a snapshot is held, any attempt to destroy it - will return an EBUY error. Each snapshot can have - multiple holds, each with a unique name. The <link - linkend="filesystems-zfs-zfs-snapshot">release</link> - command removes the hold so the snapshot can then be - deleted. Snapshots can be taken on volumes, however - they can only be cloned or rolled back, not mounted - independently.</entry> - </row> - - <row> - <entry valign="top" - id="filesystems-zfs-term-clone">Clone</entry> - - <entry>Snapshots can also be cloned; a clone is a - writable version of a snapshot, allowing the file - system to be forked as a new dataset. As with a - snapshot, a clone initially consumes no additional - space, only as new data is written to a clone and new - blocks are allocated does the apparent size of the - clone grow. As blocks are overwritten in the cloned - file system or volume, the reference count on the - previous block is decremented. The snapshot upon - which a clone is based cannot be deleted because the - clone is dependeant upon it (the snapshot is the - parent, and the clone is the child). Clones can be - <literal>promoted</literal>, reversing this - dependeancy, making the clone the parent and the - previous parent the child. This operation requires no - additional space, however it will change the way the - used space is accounted.</entry> - </row> - - <row> - <entry valign="top" - id="filesystems-zfs-term-checksum">Checksum</entry> - - <entry>Every block that is allocated is also checksummed - (which algorithm is used is a per dataset property, - see: zfs set). ZFS transparently validates the - checksum of each block as it is read, allowing ZFS to - detect silent corruption. If the data that is read - does not match the expected checksum, ZFS will attempt - to recover the data from any available redundancy - (mirrors, RAID-Z). You can trigger the validation of - all checksums using the <link - linkend="filesystems-zfs-term-scrub">scrub</link> - command. The available checksum algorithms include: - <itemizedlist> - <listitem><para>fletcher2</para></listitem> - <listitem><para>fletcher4</para></listitem> - <listitem><para>sha256</para></listitem> - </itemizedlist> The fletcher algorithms are faster, - but sha256 is a strong cryptographic hash and has a - much lower chance of a collisions at the cost of some - performance. Checksums can be disabled but it is - inadvisable.</entry> - </row> - - <row> - <entry valign="top" - id="filesystems-zfs-term-compression">Compression</entry> - - <entry>Each dataset in ZFS has a compression property, - which defaults to off. This property can be set to - one of a number of compression algorithms, which will - cause all new data that is written to this dataset to - be compressed as it is written. In addition to the - reduction in disk usage, this can also increase read - and write throughput, as only the smaller compressed - version of the file needs to be read or - written.<note> - <para>LZ4 compression is only available after &os; - 9.2</para> - </note></entry> - </row> - - <row> - <entry valign="top" - id="filesystems-zfs-term-deduplication">Deduplication</entry> - - <entry>ZFS has the ability to detect duplicate blocks of - data as they are written (thanks to the checksumming - feature). If deduplication is enabled, instead of - writing the block a second time, the reference count - of the existing block will be increased, saving - storage space. In order to do this, ZFS keeps a - deduplication table (<acronym>DDT</acronym>) in - memory, containing the list of unique checksums, the - location of that block and a reference count. When - new data is written, the checksum is calculated and - compared to the list. If a match is found, the data - is considered to be a duplicate. When deduplication - is enabled, the checksum algorithm is changed to - <acronym>SHA256</acronym> to provide a secure - cryptographic hash. ZFS deduplication is tunable; if - dedup is on, then a matching checksum is assumed to - mean that the data is identical. If dedup is set to - verify, then the data in the two blocks will be - checked byte-for-byte to ensure it is actually - identical and if it is not, the hash collision will be - noted by ZFS and the two blocks will be stored - separately. Due to the nature of the - <acronym>DDT</acronym>, having to store the hash of - each unique block, it consumes a very large amount of - memory (a general rule of thumb is 5-6 GB of ram - per 1 TB of deduplicated data). In situations - where it is not practical to have enough - <acronym>RAM</acronym> to keep the entire DDT in - memory, performance will suffer greatly as the DDT - will need to be read from disk before each new block - is written. Deduplication can make use of the L2ARC - to store the DDT, providing a middle ground between - fast system memory and slower disks. It is advisable - to consider using ZFS compression instead, which often - provides nearly as much space savings without the - additional memory requirement.</entry> - </row> - - <row> - <entry valign="top" - id="filesystems-zfs-term-scrub">Scrub</entry> - - <entry>In place of a consistency check like fsck, ZFS - has the <literal>scrub</literal> command, which reads - all data blocks stored on the pool and verifies their - checksums them against the known good checksums stored - in the metadata. This periodic check of all the data - stored on the pool ensures the recovery of any - corrupted blocks before they are needed. A scrub is - not required after an unclean shutdown, but it is - recommended that you run a scrub at least once each - quarter. ZFS compares the checksum for each block as - it is read in the normal course of use, but a scrub - operation makes sure even infrequently used blocks are - checked for silent corruption.</entry> - </row> - - <row> - <entry valign="top" - id="filesystems-zfs-term-quota">Dataset Quota</entry> - - <entry>ZFS provides very fast and accurate dataset, user - and group space accounting in addition to quotes and - space reservations. This gives the administrator fine - grained control over how space is allocated and allows - critical file systems to reserve space to ensure other - file systems do not take all of the free space. - <para>ZFS supports different types of quotas: the - dataset quota, the <link - linkend="filesystems-zfs-term-refquota">reference - quota (<acronym>refquota</acronym>)</link>, the - <link linkend="filesystems-zfs-term-userquota">user - quota</link>, and the <link - linkend="filesystems-zfs-term-groupquota"> - group quota</link>.</para> - - <para>Quotas limit the amount of space that a dataset - and all of its descendants (snapshots of the - dataset, child datasets and the snapshots of those - datasets) can consume.</para> - - <note> - <para>Quotas cannot be set on volumes, as the - <literal>volsize</literal> property acts as an - implicit quota.</para> - </note></entry> - </row> - - <row> - <entry valign="top" - id="filesystems-zfs-term-refquota">Reference - Quota</entry> - - <entry>A reference quota limits the amount of space a - dataset can consume by enforcing a hard limit on the - space used. However, this hard limit includes only - space that the dataset references and does not include - space used by descendants, such as file systems or - snapshots.</entry> - </row> - - <row> - <entry valign="top" - id="filesystems-zfs-term-userquota">User - Quota</entry> - - <entry>User quotas are useful to limit the amount of - space that can be used by the specified user.</entry> - </row> - - <row> - <entry valign="top" - id="filesystems-zfs-term-groupquota">Group - Quota</entry> - - <entry>The group quota limits the amount of space that a - specified group can consume.</entry> - </row> - - <row> - <entry valign="top" - id="filesystems-zfs-term-reservation">Dataset - Reservation</entry> - - <entry>The <literal>reservation</literal> property makes - it possible to guaranteed a minimum amount of space - for the use of a specific dataset and its descendants. - This means that if a 10 GB reservation is set on - <filename>storage/home/bob</filename>, if another - dataset tries to use all of the free space, at least - 10 GB of space is reserved for this dataset. If - a snapshot is taken of - <filename>storage/home/bob</filename>, the space used - by that snapshot is counted against the reservation. - The <link - linkend="filesystems-zfs-term-refreservation">refreservation</link> - property works in a similar way, except it - <emphasis>excludes</emphasis> descendants, such as - snapshots. - <para>Reservations of any sort are useful - in many situations, such as planning and testing the - suitability of disk space allocation in a new - system, or ensuring that enough space is available - on file systems for audio logs or system recovery - procedures and files.</para></entry> - </row> - - <row> - <entry valign="top" - id="filesystems-zfs-term-refreservation">Reference - Reservation</entry> - - <entry>The <literal>refreservation</literal> property - makes it possible to guaranteed a minimum amount of - space for the use of a specific dataset - <emphasis>excluding</emphasis> its descendants. This - means that if a 10 GB reservation is set on - <filename>storage/home/bob</filename>, if another - dataset tries to use all of the free space, at least - 10 GB of space is reserved for this dataset. In - contrast to a regular <link - linkend="filesystems-zfs-term-reservation">reservation</link>, - space used by snapshots and decendant datasets is not - counted against the reservation. As an example, if a - snapshot was taken of - <filename>storage/home/bob</filename>, enough disk - space would have to exist outside of the - <literal>refreservation</literal> amount for the - operation to succeed because descendants of the main - data set are not counted by the - <literal>refreservation</literal> amount and so do not - encroach on the space set.</entry> - </row> - - <row> - <entry valign="top" - id="filesystems-zfs-term-resilver">Resilver</entry> - - <entry>When a disk fails and must be replaced, the new - disk must be filled with the data that was lost. This - process of calculating and writing the missing data - (using the parity information distributed across the - remaining drives) to the new drive is called - Resilvering.</entry> - </row> - - </tbody> - </tgroup> - </informaltable> - </sect2> - - <sect2 id="filesystems-zfs-differences"> - <title>What Makes ZFS Different</title> - - <para>ZFS is significantly different from any previous file - system owing to the fact that it is more than just a file - system. ZFS combines the traditionally separate roles of - volume manager and file system, which provides unique - advantages because the file system is now aware of the - underlying structure of the disks. Traditional file systems - could only be created on a single disk at a time, if there - were two disks then two separate file systems would have to - be created. In a traditional hardware <acronym>RAID</acronym> - configuration, this problem was worked around by presenting - the operating system with a single logical disk made up of - the space provided by a number of disks, on top of which the - operating system placed its file system. Even in the case of - software RAID solutions like <acronym>GEOM</acronym>, the UFS - file system living on top of the <acronym>RAID</acronym> - transform believed that it was dealing with a single device. - ZFS's combination of the volume manager and the file system - solves this and allows the creation of many file systems all - sharing a pool of available storage. One of the biggest - advantages to ZFS's awareness of the physical layout of the - disks is that ZFS can grow the existing file systems - automatically when additional disks are added to the pool. - This new space is then made available to all of the file - systems. ZFS also has a number of different properties that - can be applied to each file system, creating many advantages - to creating a number of different filesystems and datasets - rather than a single monolithic filesystem.</para> - </sect2> - - <sect2 id="filesystems-zfs-quickstart"> - <title><acronym>ZFS</acronym> Quick Start Guide</title> - - <para>There is a start up mechanism that allows &os; to - mount <acronym>ZFS</acronym> pools during system - initialization. To set it, issue the following - commands:</para> - - <screen>&prompt.root; <userinput>echo 'zfs_enable="YES"' >> /etc/rc.conf</userinput> -&prompt.root; <userinput>service zfs start</userinput></screen> - - <para>The examples in this section assume three - <acronym>SCSI</acronym> disks with the device names - <devicename><replaceable>da0</replaceable></devicename>, - <devicename><replaceable>da1</replaceable></devicename>, - and <devicename><replaceable>da2</replaceable></devicename>. - Users of <acronym>SATA</acronym> hardware should instead use - <devicename><replaceable>ada</replaceable></devicename> - device names.</para> - - <sect3> - <title>Single Disk Pool</title> - - <para>To create a simple, non-redundant <acronym>ZFS</acronym> - pool using a single disk device, use - <command>zpool</command>:</para> - - <screen>&prompt.root; <userinput>zpool create <replaceable>example</replaceable> <replaceable>/dev/da0</replaceable></userinput></screen> - - <para>To view the new pool, review the output of - <command>df</command>:</para> - - <screen>&prompt.root; <userinput>df</userinput> -Filesystem 1K-blocks Used Avail Capacity Mounted on -/dev/ad0s1a 2026030 235230 1628718 13% / -devfs 1 1 0 100% /dev -/dev/ad0s1d 54098308 1032846 48737598 2% /usr -example 17547136 0 17547136 0% /example</screen> - - <para>This output shows that the <literal>example</literal> - pool has been created and <emphasis>mounted</emphasis>. It - is now accessible as a file system. Files may be created - on it and users can browse it, as seen in the following - example:</para> - - <screen>&prompt.root; <userinput>cd /example</userinput> -&prompt.root; <userinput>ls</userinput> -&prompt.root; <userinput>touch testfile</userinput> -&prompt.root; <userinput>ls -al</userinput> -total 4 -drwxr-xr-x 2 root wheel 3 Aug 29 23:15 . -drwxr-xr-x 21 root wheel 512 Aug 29 23:12 .. --rw-r--r-- 1 root wheel 0 Aug 29 23:15 testfile</screen> - - <para>However, this pool is not taking advantage of any - <acronym>ZFS</acronym> features. To create a dataset on - this pool with compression enabled:</para> - - <screen>&prompt.root; <userinput>zfs create example/compressed</userinput> -&prompt.root; <userinput>zfs set compression=gzip example/compressed</userinput></screen> - - <para>The <literal>example/compressed</literal> dataset is now - a <acronym>ZFS</acronym> compressed file system. Try - copying some large files to <filename - class="directory">/example/compressed</filename>.</para> - - <para>Compression can be disabled with:</para> - - <screen>&prompt.root; <userinput>zfs set compression=off example/compressed</userinput></screen> - - <para>To unmount a file system, issue the following command - and then verify by using <command>df</command>:</para> - - <screen>&prompt.root; <userinput>zfs umount example/compressed</userinput> -&prompt.root; <userinput>df</userinput> -Filesystem 1K-blocks Used Avail Capacity Mounted on -/dev/ad0s1a 2026030 235232 1628716 13% / -devfs 1 1 0 100% /dev -/dev/ad0s1d 54098308 1032864 48737580 2% /usr -example 17547008 0 17547008 0% /example</screen> - - <para>To re-mount the file system to make it accessible - again, and verify with <command>df</command>:</para> - - <screen>&prompt.root; <userinput>zfs mount example/compressed</userinput> -&prompt.root; <userinput>df</userinput> -Filesystem 1K-blocks Used Avail Capacity Mounted on -/dev/ad0s1a 2026030 235234 1628714 13% / -devfs 1 1 0 100% /dev -/dev/ad0s1d 54098308 1032864 48737580 2% /usr -example 17547008 0 17547008 0% /example -example/compressed 17547008 0 17547008 0% /example/compressed</screen> - - <para>The pool and file system may also be observed by viewing - the output from <command>mount</command>:</para> - - <screen>&prompt.root; <userinput>mount</userinput> -/dev/ad0s1a on / (ufs, local) -devfs on /dev (devfs, local) -/dev/ad0s1d on /usr (ufs, local, soft-updates) -example on /example (zfs, local) -example/data on /example/data (zfs, local) -example/compressed on /example/compressed (zfs, local)</screen> - - <para><acronym>ZFS</acronym> datasets, after creation, may be - used like any file systems. However, many other features - are available which can be set on a per-dataset basis. In - the following example, a new file system, - <literal>data</literal> is created. Important files will be - stored here, the file system is set to keep two copies of - each data block:</para> - - <screen>&prompt.root; <userinput>zfs create example/data</userinput> -&prompt.root; <userinput>zfs set copies=2 example/data</userinput></screen> - - <para>It is now possible to see the data and space utilization - by issuing <command>df</command>:</para> - - <screen>&prompt.root; <userinput>df</userinput> -Filesystem 1K-blocks Used Avail Capacity Mounted on -/dev/ad0s1a 2026030 235234 1628714 13% / -devfs 1 1 0 100% /dev -/dev/ad0s1d 54098308 1032864 48737580 2% /usr -example 17547008 0 17547008 0% /example -example/compressed 17547008 0 17547008 0% /example/compressed -example/data 17547008 0 17547008 0% /example/data</screen> - - <para>Notice that each file system on the pool has the same - amount of available space. This is the reason for using - <command>df</command> in these examples, to show that the - file systems use only the amount of space they need and all - draw from the same pool. The <acronym>ZFS</acronym> file - system does away with concepts such as volumes and - partitions, and allows for several file systems to occupy - the same pool.</para> - - <para>To destroy the file systems and then destroy the pool as - they are no longer needed:</para> - - <screen>&prompt.root; <userinput>zfs destroy example/compressed</userinput> -&prompt.root; <userinput>zfs destroy example/data</userinput> -&prompt.root; <userinput>zpool destroy example</userinput></screen> - - </sect3> - - <sect3> - <title><acronym>ZFS</acronym> RAID-Z</title> - - <para>There is no way to prevent a disk from failing. One - method of avoiding data loss due to a failed hard disk is to - implement <acronym>RAID</acronym>. <acronym>ZFS</acronym> - supports this feature in its pool design. RAID-Z pools - require 3 or more disks but yield more usable space than - mirrored pools.</para> - - <para>To create a <acronym>RAID</acronym>-Z pool, issue the - following command and specify the disks to add to the - pool:</para> - - <screen>&prompt.root; <userinput>zpool create storage raidz da0 da1 da2</userinput></screen> - - <note> - <para>&sun; recommends that the number of devices used in - a <acronym>RAID</acronym>-Z configuration is between - three and nine. For environments requiring a single pool - consisting of 10 disks or more, consider breaking it up - into smaller <acronym>RAID</acronym>-Z groups. If only - two disks are available and redundancy is a requirement, - consider using a <acronym>ZFS</acronym> mirror. Refer to - &man.zpool.8; for more details.</para> - </note> - - <para>This command creates the <literal>storage</literal> - zpool. This may be verified using &man.mount.8; and - &man.df.1;. This command makes a new file system in the - pool called <literal>home</literal>:</para> - - <screen>&prompt.root; <userinput>zfs create storage/home</userinput></screen> - - <para>It is now possible to enable compression and keep extra - copies of directories and files using the following - commands:</para> - - <screen>&prompt.root; <userinput>zfs set copies=2 storage/home</userinput> -&prompt.root; <userinput>zfs set compression=gzip storage/home</userinput></screen> - - <para>To make this the new home directory for users, copy the - user data to this directory, and create the appropriate - symbolic links:</para> - - <screen>&prompt.root; <userinput>cp -rp /home/* /storage/home</userinput> -&prompt.root; <userinput>rm -rf /home /usr/home</userinput> -&prompt.root; <userinput>ln -s /storage/home /home</userinput> -&prompt.root; <userinput>ln -s /storage/home /usr/home</userinput></screen> - - <para>Users should now have their data stored on the freshly - created <filename - class="directory">/storage/home</filename>. Test by - adding a new user and logging in as that user.</para> - - <para>Try creating a snapshot which may be rolled back - later:</para> - - <screen>&prompt.root; <userinput>zfs snapshot storage/home@08-30-08</userinput></screen> - - <para>Note that the snapshot option will only capture a real - file system, not a home directory or a file. The - <literal>@</literal> character is a delimiter used between - the file system name or the volume name. When a user's - home directory gets trashed, restore it with:</para> - - <screen>&prompt.root; <userinput>zfs rollback storage/home@08-30-08</userinput></screen> - - <para>To get a list of all available snapshots, run - <command>ls</command> in the file system's - <filename class="directory">.zfs/snapshot</filename> - directory. For example, to see the previously taken - snapshot:</para> - - <screen>&prompt.root; <userinput>ls /storage/home/.zfs/snapshot</userinput></screen> - - <para>It is possible to write a script to perform regular - snapshots on user data. However, over time, snapshots - may consume a great deal of disk space. The previous - snapshot may be removed using the following command:</para> - - <screen>&prompt.root; <userinput>zfs destroy storage/home@08-30-08</userinput></screen> - - <para>After testing, <filename - class="directory">/storage/home</filename> can be made the - real <filename class="directory">/home</filename> using - this command:</para> - - <screen>&prompt.root; <userinput>zfs set mountpoint=/home storage/home</userinput></screen> - - <para>Run <command>df</command> and - <command>mount</command> to confirm that the system now - treats the file system as the real - <filename class="directory">/home</filename>:</para> - - <screen>&prompt.root; <userinput>mount</userinput> -/dev/ad0s1a on / (ufs, local) -devfs on /dev (devfs, local) -/dev/ad0s1d on /usr (ufs, local, soft-updates) -storage on /storage (zfs, local) -storage/home on /home (zfs, local) -&prompt.root; <userinput>df</userinput> -Filesystem 1K-blocks Used Avail Capacity Mounted on -/dev/ad0s1a 2026030 235240 1628708 13% / -devfs 1 1 0 100% /dev -/dev/ad0s1d 54098308 1032826 48737618 2% /usr -storage 26320512 0 26320512 0% /storage -storage/home 26320512 0 26320512 0% /home</screen> - - <para>This completes the <acronym>RAID</acronym>-Z - configuration. To get status updates about the file systems - created during the nightly &man.periodic.8; runs, issue the - following command:</para> - - <screen>&prompt.root; <userinput>echo 'daily_status_zfs_enable="YES"' >> /etc/periodic.conf</userinput></screen> - </sect3> - - <sect3> - <title>Recovering <acronym>RAID</acronym>-Z</title> - - <para>Every software <acronym>RAID</acronym> has a method of - monitoring its <literal>state</literal>. The status of - <acronym>RAID</acronym>-Z devices may be viewed with the - following command:</para> - - <screen>&prompt.root; <userinput>zpool status -x</userinput></screen> - *** DIFF OUTPUT TRUNCATED AT 1000 LINES ***help
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