document/TranslateProject
2
0
Fork 0
mirror of https://github.com/LCTT/TranslateProject.git synced 2024-12-26 21:30:55 +08:00
Code Issues Packages Projects Releases Wiki Activity

Merge pull request #20765 from Chao-zhi/translate-MjAyMDEyMzAgQ2hvb3NlIGJldHdlZW4gQnRyZnMgYW5kIExWTS1leHQ0Lm1kCg==

Browse Source 
translate done: 20201230 Choose between Btrfs and LVM-ext4.md
This commit is contained in:
Xingyu.Wang 2021-01-18 22:19:31 +08:00 committed by GitHub
commit 83248eb6c7
No known key found for this signature in database
GPG Key ID: 4AEE18F83AFDEB23
2 changed files with 150 additions and 150 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

150
sources/tech/20201230 Choose between Btrfs and LVM-ext4.md
View File

@ -1,150 +0,0 @@
[#]: collector: (lujun9972)
[#]: translator: (Chao-zhi)
[#]: reviewer: ( )
[#]: publisher: ( )
[#]: url: ( )
[#]: subject: (Choose between Btrfs and LVM-ext4)
[#]: via: (https://fedoramagazine.org/choose-between-btrfs-and-lvm-ext4/)
[#]: author: (Troy Curtis Jr https://fedoramagazine.org/author/troycurtisjr/)
Choose between Btrfs and LVM-ext4
======
![][1]
Photo by [Raul Petri][2] on [Unsplash][3]
[Fedora 33][4] introduced a new default filesystem in desktop variants, [Btrfs][5]. After years of Fedora using [ext4][6] on top of [Logical Volume Manager (LVM)][7] volumes, this is a big shift. Changing the default file system requires [compelling reasons][8]. While Btrfs is an exciting next-generation file system, ext4 on LVM is well established and stable. This guide aims to explore the high-level features of each and make it easier to choose between Btrfs and LVM-ext4.
### In summary
The simplest advice is to stick with the defaults. A fresh Fedora 33 install defaults to Btrfs and upgrading a previous Fedora release continues to use whatever was initially installed, typically LVM-ext4. For an existing Fedora user, the cleanest way to get Btrfs is with a fresh install. However, a fresh install is much more disruptive than a simple upgrade. Unless there is a specific need, this disruption could be unnecessary. The Fedora development team carefully considered both defaults, so be confident with either choice.
### What about all the other file systems?
There are a [large number of file systems for Linux systems][9]. The number explodes after adding in combinations of volume managers, encryption methods, and storage mechanisms . So why focus on Btrfs and LVM-ext4? For the Fedora audience these two setups are likely to be the most common. Ext4 on top of LVM became the default disk layout in Fedora 11, and ext3 on top of LVM came before that.
Now that Btrfs is the default for Fedora 33, the vast majority of existing users will be looking at whether they should stay where they are or make the jump forward. Faced with a fresh Fedora 33 install, experienced Linux users may wonder whether to use this new file system or fall back to what they are familiar with. So out of the wide field of possible storage options, many Fedora users will wonder how to choose between Btrfs and LVM-ext4.
### Commonalities
Despite core differences between the two setups, Btrfs and LVM-ext4 actually have a lot in common. Both are mature and well-tested storage technologies. LVM has been in continuous use since the early days of Fedora Core and ext4 became the [default in 2009 with Fedora 11][10]. Btrfs merged into the mainline Linux kernel in 2009 and [Facebook uses it widely][11]. SUSE Linux Enterprise 12 made it the [default in 2014][12]. So there is plenty of production run time there as well.
Both systems do a great job preventing file system corruption due to unexpected power outages, even though the way they accomplish it is different. Supported configurations include single drive setups as well as spanning multiple devices, and both are capable of creating nearly instant snapshots. A variety of tools exist to help manage either system, both with the command line and graphical interfaces. Either solution works equally well on home desktops and on high-end servers.
### Advantages of LVM-ext4
![Structure of ext4 on LVM][13]
The [ext4 file system][14] focuses on high-performance and scalability, without a lot of extra frills. It is effective at preventing fragmentation over extended periods of time and provides [nice tools][15] for when it does happen. Ext4 is rock solid because it built on the previous ext3 file system, bringing with it all the years of in-system testing and bug fixes.
Most of the advanced capabilities in the LVM-ext4 setup come from LVM itself. LVM sits “below” the file system, which means it supports any file system. Logical volumes (LV) are generic block devices so [virtual machines can use them directly.][16] This flexibility allows each logical volume to use the right file system, with the right options, for a variety of situations. This layered approach also honors the Unix philosophy of small tools working together.
The [volume group][17] (VG) abstraction from the hardware allows LVM to create flexible logical volumes. Each LV pulls from the same storage pool but has its own configuration. Resizing volumes is a lot easier than resizing physical partitions as there are no limitation of ordered placement of the data. LVM [physical volumes][18] (PV) can be any number of partitions and can even move between devices while the system is running.
LVM supports read-only and read-write [snapshots][19], which make it easy to create consistent backups from active systems. Each snapshot has a defined size, and a change to the source or snapshot volume use space from there. Alternately, logical volumes can also be part of a [thinly provisioned pool][20]. This allows snapshots to automatically use data from a pool instead of consuming fixed sized chunks defined at volume creation.
#### Multiple devices with LVM
LVM really shines when there are multiple devices. It has native support for most [RAID levels][21] and each logical volume can have a different RAID level. LVM will automatically choose appropriate physical devices for the RAID configuration or the user can specify it directly. Basic RAID support includes data striping for performance ([RAID0][22]) and mirroring for redundancy ([RAID1][23]). Logical volumes can also use advanced setups like [RAID5][24], [RAID6][25], and [RAID10][26]. LVM RAID support is mature because under the hood LVM uses the same [device-mapper (dm)][27] and [multiple-device (md)][28] kernel support used by [mdadm][29].
Logical volumes can also be [cached volumes][30] for systems with both fast and slow drives. A classic example is a combination of SSD and spinning-disk drives. Cached volumes use faster drives for more frequently accessed data (or as a write cache), and the slower drive for bulk data.
The large number of stable features in LVM and the reliable performance of ext4 are a testament to how long they have been in use. Of course, with more features comes complexity. It can be challenging to find the right options for the right feature when configuring LVM. For single drive desktop systems, features of LVM like RAID and cache volumes don’t apply. However, logical volumes are more flexible than physical partitions and snapshots are useful. For normal desktop use, the complexity of LVM can also be a barrier to recovering from issues a typical user might encounter.
### Advantages of Btrfs
![Btrfs Structure][31]
Lessons learned from previous generations guided the features built into [Btrfs][5]. Unlike ext4, it can directly span multiple devices, so it brings along features typically found only in volume managers. It also has features that are unique in the Linux file system space ([ZFS][32] has a similar feature set, but [don’t expect it in the Linux kernel][33]).
#### Key Btrfs features
Perhaps the most important feature is the checksumming of all data. Checksumming, along with copy-on-write, provides the [key method][34] of ensuring file system integrity after unexpected power loss. More uniquely, checksumming can detect errors in the data itself. Silent data corruption, sometimes referred to as [bitrot][35], is more common that most people realize. Without active validation, corruption can end up propagating to all available backups. This leaves the user with no valid copies. By transparently checksumming all data, Btrfs is able to immediately detect any such corruption. Enabling the right [dup or raid option][36] allows the file system to transparently fix the corruption as well.
[Copy-on-write][37] (COW) is also a fundamental feature of Btrfs, as it is critical in providing file system integrity and instant subvolume snapshots. Snapshots automatically share underlying data when created from common subvolumes. Additionally, after-the-fact [deduplication][38] uses the same technology to eliminate identical data blocks. Individual files can use COW features by calling _cp_ with the [reflink option][39]. Reflink copies are especially useful for copying large files, such as virtual machine images, that tend to have mostly identical data over time.
Btrfs supports spanning multiple devices with no volume manager required. Multiple device support unlocks data mirroring for redundancy and striping for performance. There is also experimental support for more advanced RAID levels, such as [RAID5][24] and [RAID6][25]. Unlike standard RAID setups, the Btrfs _raid1_ option actually allows an odd number of devices. For example, it can use 3 devices, even if they are are different sizes.
All RAID and dup options are specified at the file system level. As a consequence, individual subvolumes cannot use different options. Note that using the RAID1 option with multiple devices means that all data in the volume is available even if one device fails and the checksum feature maintains the integrity of the data itself. That is beyond what current typical RAID setups can provide.
#### Additional features
Btrfs also enables quick and easy remote backups. Subvolume snapshots can be [sent to a remote system][40] for storage. By leveraging the inherent COW meta-data in the file system, these transfers are efficient by only sending incremental changes from previously sent snapshots. User applications such as [snapper][41] make it easy to manage these snapshots.
Additionally, a Btrfs volume can have [transparent compression][42] and _[chattr +c][43]_ will mark individual files or directories for compression. Not only does compression reduce the space consumed by data, but it helps extend the life of SSDs by reducing the volume of write operations. Compression certainly introduces additional CPU overhead, but a lot of options are available to dial in the right trade-offs.
The integration of file system and volume manager functions by Btrfs means that overall maintenance is simpler than LVM-ext4. Certainly this integration comes with less flexibility, but for most desktop, and even server, setups it is more than sufficient.
### Btrfs on LVM
Btrfs can [convert an ext3/ext4 file system in place][44]. In-place conversion means no data to copy out and then back in. The data blocks themselves are not even modified. As a result, one option for an existing LVM-ext4 systems is to leave LVM in place and simply convert ext4 over to Btrfs. While doable and supported, there are reasons why this isn’t the best option.
Some of the appeal of Btrfs is the easier management that comes with a file system integrated with a volume manager. By running on top of LVM, there is still some other volume manager in play for any system maintenance. Also, LVM setups typically have multiple fixed sized logical volumes with independent file systems. While Btrfs supports multiple volumes in a given computer, many of the nice features expect a single volume with multiple subvolumes. The user is still stuck manually managing fixed sized LVM volumes if each one has an independent Btrfs volume. Though, the ability to shrink mounted Btrfs filesystems does make working with fixed sized volumes less painful. With online shrink there is no need to boot a [live image][45].
The physical locations of logical volumes must be carefully considered when using the multiple device support of Btrfs. To Btrfs, each LV is a separate physical device and if that is not actually the case, then certain data availability features might make the wrong decision. For example, using _raid1_ for data typically provides protection if a single drive fails. If the actual logical volumes are on the same physical device, then there is no redundancy.
If there is a strong need for some particular LVM feature, such as raw block devices or cached logical volumes, then running Btrfs on top of LVM makes sense. In this configuration, Btrfs still provides most of its advantages such as checksumming and easy sending of incremental snapshots. While LVM has some operational overhead when used, it is no more so with Btrfs than with any other file system.
### Wrap up
When trying to choose between Btrfs and LVM-ext4 there is no single right answer. Each user has unique requirements, and the same user may have different systems with different needs. Take a look at the feature set of each configuration, and decide if there is something compelling about one over the other. If not, there is nothing wrong with sticking with the defaults. There are excellent reasons to choose either setup.
--------------------------------------------------------------------------------
via: https://fedoramagazine.org/choose-between-btrfs-and-lvm-ext4/
作者：[Troy Curtis Jr][a]
选题：[lujun9972][b]
译者：[Chao-zhi](https://github.com/Chao-zhi)
校对：[校对者ID](https://github.com/校对者ID)
本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
[a]: https://fedoramagazine.org/author/troycurtisjr/
[b]: https://github.com/lujun9972
[1]: https://fedoramagazine.org/wp-content/uploads/2020/12/btrfs-lvm-ext4-816x345.jpg
[2]: https://unsplash.com/@raulpetri?utm_source=unsplash&utm_medium=referral&utm_content=creditCopyText
[3]: https://unsplash.com/?utm_source=unsplash&utm_medium=referral&utm_content=creditCopyText
[4]: https://fedoramagazine.org/announcing-fedora-33/
[5]: https://btrfs.wiki.kernel.org/index.php/Main_Page
[6]: https://ext4.wiki.kernel.org/index.php/Main_Page
[7]: https://man7.org/linux/man-pages/man8/lvm.8.html
[8]: https://fedoraproject.org/wiki/Changes/BtrfsByDefault
[9]: https://man7.org/linux/man-pages/man5/filesystems.5.html
[10]: https://docs.fedoraproject.org/en-US/Fedora/11/html/Release_Notes/index.html#sect-Release_Notes-Fedora_11_Overview
[11]: https://facebookmicrosites.github.io/btrfs/docs/btrfs-facebook.html
[12]: https://www.suse.com/releasenotes/x86_64/SUSE-SLES/12/#fate-317221
[13]: https://fedoramagazine.org/wp-content/uploads/2020/12/ext4-on-LVM.jpg
[14]: https://opensource.com/article/18/4/ext4-filesystem
[15]: https://man7.org/linux/man-pages/man8/e4defrag.8.html
[16]: https://libvirt.org/storage.html#StorageBackendLogical
[17]: https://www.redhat.com/sysadmin/create-volume-group
[18]: https://www.redhat.com/sysadmin/create-physical-volume
[19]: https://tldp.org/HOWTO/LVM-HOWTO/snapshotintro.html
[20]: https://man7.org/linux/man-pages/man7/lvmthin.7.html
[21]: https://rhea.dev/articles/2018-08/LVM-RAID-on-Fedora
[22]: https://en.wikipedia.org/wiki/Standard_RAID_levels#RAID_0
[23]: https://en.wikipedia.org/wiki/Standard_RAID_levels#RAID_1
[24]: https://en.wikipedia.org/wiki/Standard_RAID_levels#RAID_5
[25]: https://en.wikipedia.org/wiki/Standard_RAID_levels#RAID_6
[26]: https://en.wikipedia.org/wiki/Non-standard_RAID_levels#Linux_MD_RAID_10
[27]: https://man7.org/linux/man-pages/man8/dmsetup.8.html
[28]: https://man7.org/linux/man-pages/man4/md.4.html
[29]: https://fedoramagazine.org/managing-raid-arrays-with-mdadm/
[30]: https://man7.org/linux/man-pages/man7/lvmcache.7.html
[31]: https://fedoramagazine.org/wp-content/uploads/2020/12/Btrfs-Volume.jpg
[32]: https://en.wikipedia.org/wiki/ZFS
[33]: https://itsfoss.com/linus-torvalds-zfs/
[34]: https://btrfs.wiki.kernel.org/index.php/FAQ#Can_I_have_nodatacow_.28or_chattr_.2BC.29_but_still_have_checksumming.3F
[35]: https://arstechnica.com/information-technology/2014/01/bitrot-and-atomic-cows-inside-next-gen-filesystems/
[36]: https://man7.org/linux/man-pages/man8/mkfs.btrfs.8.html#DUP_PROFILES_ON_A_SINGLE_DEVICE
[37]: https://en.wikipedia.org/wiki/Copy-on-write
[38]: https://btrfs.wiki.kernel.org/index.php/Deduplication
[39]: https://btrfs.wiki.kernel.org/index.php/UseCases#How_do_I_copy_a_large_file_and_utilize_COW_to_keep_it_from_actually_being_copied.3F
[40]: https://fedoramagazine.org/btrfs-snapshots-backup-incremental/
[41]: http://snapper.io/
[42]: https://btrfs.wiki.kernel.org/index.php/Compression
[43]: https://www.man7.org/linux/man-pages/man1/chattr.1.html
[44]: https://btrfs.wiki.kernel.org/index.php/Conversion_from_Ext3
[45]: https://fedoramagazine.org/reclaim-hard-drive-space-with-lvm/

150
translated/tech/20201230 Choose between Btrfs and LVM-ext4.md Normal file
View File

@ -0,0 +1,150 @@
[#]: collector: (lujun9972)
[#]: translator: (Chao-zhi)
[#]: reviewer: ( )
[#]: publisher: ( )
[#]: url: ( )
[#]: subject: (Choose between Btrfs and LVM-ext4)
[#]: via: (https://fedoramagazine.org/choose-between-btrfs-and-lvm-ext4/)
[#]: author: (Troy Curtis Jr https://fedoramagazine.org/author/troycurtisjr/)
Btrfs 和 LVM-ext4 该如何选择？
======
![][1]
图片来自 [Raul Petri][2] 发表在 [Unsplash][3]
[Fedora 33][4] 在桌面版本 [Btrfs][5] 中引入了新的默认文件系统。多年以来，Fedora 一直在 [Logical Volume Manager（LVM）][7] 卷之上使用 [ext4][6]，引入 Brtfs 对 Fedora 来说是一个很大的转变。更改默认文件系统需要[令人信服的原因 ][8]。虽然 Btrfs 是令人兴奋的下一代文件系统，但 LVM 上的 ext4 已经建立并稳定。本指南旨在探索每种功能的高级特性，并使其更容易在 Btrfs 和 LVM-ext4 之间进行选择。
### 先说结论
最简单的建议是坚持使用默认值。全新的 Fedora 33 安装默认为 Btrfs，升级之前的 Fedora 版本将继续使用最初安装的版本，通常是 lvm-ext4。对于现有的 Fedora 用户来说，获取 Btrfs 的最简单方式是全新安装。然而，全新安装比简单升级更具破坏性。除非有特殊需要，否则这种干扰可能是不必要的。Fedora 开发团队仔细考虑了这两个缺省值，因此对任何一个选择都要有信心。
### 那么所有其他文件系统呢？
现在有很多 [Linux 系统的文件系统 ][9]。在添加卷管理器、加密方法和存储机制的组合后，这一数字呈爆炸式增长。那么，为什么要关注 btrfs 和 lvm-ext4 呢？对于 Fedora 的用户来说，这两种设置可能是最常见的。LVM 之上的 ext4 成为 Fedora 11 中的默认磁盘布局，在此之前则使用的是 ext3。
既然 Btrfs 是 Fedora 33 的默认设置，那么绝大多数现有用户将会考虑是应该原地踏步还是向前更新。面对全新的 Fedora 33 安装，有经验的 Linux 用户可能会想知道是使用这个新的文件系统，还是退回到他们熟悉的文件系统。因此，在众多可能的存储选项中，许多 Fedora 用户会想知道如何在 Btrfs 和 lvm-ext4 之间进行选择。
### 两者的共性
尽管两个设置之间存在核心差异，但 Btrfs 和 lvm-ext4 实际上有很多共同之处。两者都是成熟且经过充分测试的存储技术。从 Fedora Core 的早期开始，LVM 就一直在使用，ext4 在 2009 年成为 Fedora 11 的默认版本 [10]。Btrfs 在 2009 年并入主流 Linux 内核，并且 [Facebook 广泛使用该文件系统 ][11]。SUSE Linux Enterprise 12 使其成为 [2014 年的默认版本 ][12]。因此，他们在生产力工具上都有充分的运行时间。
这两个系统都能很好地防止因意外停电而导致的文件系统损坏，尽管它们的实现方式不同。支持的配置包括使用单个驱动器和跨多个磁盘驱动器，并且这两种配置都能够创建近乎即时的快照。通过命令行和图形界面，存在多种工具来帮助管理这两个系统。这两种解决方案在家用台式机和高端服务器上都同样有效。
### LVM-ext4 的优势。
![LVM 上 ext4 的结构 ][13]。
[ext4 文件系统 ][14] 专注于高性能和可伸缩性，没有太多额外的花哨之处。它在很长一段时间内有效地防止碎片化，并提供了[很好的工具 ][15] 来判断何时出现碎片化。Ext4 是坚如磐石的，因为它构建在以前的 ext3 文件系统之上，带来了多年的系统内测试和错误修复。
Lvm-ext4 设置中的大多数高级功能都来自 LVM 本身。LVM 位于文件系统的“下方”，这意味着它支持任何文件系统。逻辑卷 （LV） 是通用的块设备，因此[虚拟机可以直接使用它们。][16] 这种灵活性允许每个逻辑卷使用正确的文件系统和正确的选项，以应对各种情况。这种分层方法还遵循了小工具协同工作的 Unix 理念。
硬件的[卷组 ][17]（VG） 抽象允许 LVM 创建灵活的逻辑卷。每个 LV 从同一存储池拉入，但具有自己的配置。调整卷的大小比调整物理分区的大小容易得多，因为数据的有序放置没有限制。LVM [物理卷 ][18]（PV） 可以是任意数量的分区，甚至可以在系统运行时在设备之间移动。
LVM 支持只读和读写[快照 ][19]，这使得从活动系统创建一致的备份变得很容易。每个快照都有一个定义的大小，更改源卷或快照卷将占用其中的空间。又或者，逻辑卷也可以是[精简资源调配池 ][20] 的一部分。这允许快照自动使用池中的数据，而不是使用在创建卷时定义的固定大小的区块。
#### 有多个磁盘驱动器的 LVM
当有多个设备时，LVM 确实会焕发能量。它具有对大多数 [RAID 级别 ][21] 的本地支持，每个逻辑卷可以具有不同的 RAID 级别。LVM 将自动为 RAID 配置选择适当的物理设备，或者用户可以直接指定它。基本的 RAID 支持包括用于性能的数据分条 （[RAID0][22]） 和用于冗余的镜像 （[RAID1][23]）。逻辑卷也可以使用 [RAID5][24]，[RAID6][25] 和 [RAID10][26] 等高级设置。LVM RAID 支持已经成熟，因为 LVM 在后台使用了 [mdadm][29] 使用的相同的 [device-mapper（dm）][27] 和 [multi-device（md）][28] 内核支持。
对于具有快速和慢速驱动器的系统，逻辑卷也可以是[缓存的卷 ][30]。经典示例是 SSD 和传统磁盘驱动器的组合。高速缓存的卷使用更快的驱动器来存储更频繁访问的数据（或用作写缓存），而慢速的驱动器使用批量数据。
LVM 中大量稳定的功能以及 ext4 的可靠性在既往的使用中早已被证明了。当然，具有更多功能会带来复杂性。在配置 LVM 时，为正确的功能找到正确的选项可能具有挑战性。对于单驱动器台式机系统，LVM 的功能（例如 RAID 和缓存卷）不适用。但是，逻辑卷比物理分区更灵活，快照也很有用。对于正常的桌面使用，LVM 的复杂性会成为常见的用户从可能遇到的问题中恢复的障碍。
### Btrfs 的优势
![Btrfs 结构 ][31]
从前几代文件系统中学到的经验指导了 [Btrfs][5] 内置的功能的设计。与 ext4 不同，它可以直接跨越多个设备，因此它具有通常仅在卷管理器中才能找到的功能。它还具有 Linux 文件系统空间中独有的功能 （[ZFS][32] 具有相似的功能集，但[不要在 Linux 内核中期望它 ][33]）。
#### Btrfs 的主要功能
也许最重要的功能是所有数据的校验和。校验和与写时复制一起提供了 [key 方法 ][34]，可确保在意外断电后确保文件系统的完整性。更独特的是，校验和可以检测数据本身中的错误。悄然的数据损坏（有时也称为 [bitrot][35]） 是大多数人意识到的更常见的现象。没有主动验证，损坏最终可能会传播到所有可用备份。这使用户没有有效的副本。通过透明地校验所有数据，Btrfs 能够立即检测到任何此类损坏。启用正确的 [dup 或 raid 选项 ][36]，文件系统也可以透明地修复损坏。
[写入时复制 ][37]（COW） 也是 Btrfs 的基本功能，因为它在提供文件系统完整性和即时子卷快照方面至关重要。从通用子卷创建快照后，快照会自动共享基础数据。另外，事后[重复数据删除 ][38] 使用相同的技术来消除相同的数据块。单个文件可以通过使用 [reflink 选项 ][39] 调用 _cp_ 来使用 COW 功能。Reflink 副本对于复制大型文件（例如虚拟机映像）特别有用，例如，随着时间的流逝，这些文件通常具有几乎相同的数据。
Btrfs 支持跨多个设备，而无需卷管理器。多设备支持可解锁数据镜像以实现冗余，而条带化则可提高性能。实验上还支持更高级的 RAID 级别，例如 [RAID 5][24] 和 [RAID 6][25]。与标准 RAID 设置不同，Btrfs _raid1_ 选项实际上允许奇数个设备。例如，即使它们的大小不同，它也可以使用 3 个设备。
所有 RAID 和 dup 选项都在文件系统级别指定。因此，各个子卷不能使用不同的选项。请注意，将 RAID 1 选项与多个设备一起使用意味着即使一个设备发生故障，并且校验和功能仍可保持数据本身的完整性，卷中的所有数据均可用。这超出了当前典型的 RAID 设置所能提供的范围。
#### 附加功能
Btrfs 还支持快速简便的远程备份。子卷快照可以[发送到远程系统 ][40] 进行存储。通过利用文件系统中固有的 COW 元数据，这些传输通过仅发送先前发送的快照中的增量更改而非常有效。诸如 [snapper][41] 之类的用户应用程序使管理这些快照变得容易。
另外，Btrfs 卷可以具有[透明压缩 ][42]，并且 _ [chattr + c][43] _ 将标记单个文件或目录以进行压缩。压缩不仅可以减少数据消耗的空间，还可以通过减少写入操作量来帮助延长 SSD 的寿命。压缩当然会带来额外的 CPU 开销，但是有很多选项可用于权衡取舍。
Btrfs 集成了文件系统和卷管理器功能，这意味着总体维护比 LVM-ext4 更简单。当然，这种集成的灵活性较低，但是对于大多数台式机甚至服务器而言，设置已足够。
### LVM 上使用 Btrfs
Btrfs 可以[就地转换 ext3/ext4 文件系统 ][44]。就地转换意味着没有数据可以复制出来然后再返回。数据块本身甚至都没有被修改。结果，现有 LVM-ext4 系统的一种选择是将 LVM 保留在原处，然后简单地将 ext4 转换为 Btrfs。虽然可行且受支持，但有一些原因使它不是最佳选择。
Btrfs 的吸引力之一是与卷管理器集成的文件系统附带的更轻松的管理。通过在 LVM 之上运行，还可以使用其他卷管理器来进行任何系统维护。同样，LVM 设置通常具有多个具有独立文件系统的固定大小的逻辑卷。虽然 Btrfs 在给定的计算机上支持多个卷，但是许多不错的功能都希望单个卷具有多个子卷。如果每个 LVM 卷都有一个独立的 Btrfs 卷，则用户仍然无法手动管理固定大小的 LVM 卷。但是，收缩挂载的 Btrfs 文件系统的能力确实使处理固定大小的卷的工作变得更轻松。通过在线收缩，无需启动[实时镜像 ][45]。
使用 Btrfs 的多设备支持时，必须仔细考虑逻辑卷的物理位置。对于 Btrfs 而言，每个 LV 都是一个单独的物理设备，如果实际情况并非如此，则某些数据可用性功能可能会做出错误的决定。例如，如果单个驱动器发生故障，对数据使用 _raid1_ 通常可以提供保护。如果实际逻辑卷在同一物理设备上，则没有冗余。
如果强烈需要某些特定的 LVM 功能，例如原始块设备或高速缓存的逻辑卷，则在 LVM 之上运行 Btrfs 是有意义的。在这种配置下，Btrfs 仍然提供其大多数优点，例如校验和和易于发送的增量快照。尽管使用 LVM 会产生一些操作开销，但 Btrfs 的这种开销并不比任何其他文件系统大。
### 总结
当尝试在 Btrfs 和 LVM-ext4 之间进行选择时，没有一个正确的答案。每个用户都有独特的要求，并且同一用户可能拥有具有不同需求的不同系统。看一下每个配置的功能集，并确定是否有令人心动的功能。如果没有，坚持默认值没有错。选择这两种设置都有很好的理由。
--------------------------------------------------------------------------------
via: https://fedoramagazine.org/choose-between-btrfs-and-lvm-ext4/
作者：[Troy Curtis Jr][a]
选题：[lujun9972][b]
译者：[Chao-zhi](https://github.com/Chao-zhi)
校对：[校对者ID](https://github.com/校对者ID)
本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
[a]: https://fedoramagazine.org/author/troycurtisjr/
[b]: https://github.com/lujun9972
[1]: https://fedoramagazine.org/wp-content/uploads/2020/12/btrfs-lvm-ext4-816x345.jpg
[2]: https://unsplash.com/@raulpetri?utm_source=unsplash&utm_medium=referral&utm_content=creditCopyText
[3]: https://unsplash.com/?utm_source=unsplash&utm_medium=referral&utm_content=creditCopyText
[4]: https://fedoramagazine.org/announcing-fedora-33/
[5]: https://btrfs.wiki.kernel.org/index.php/Main_Page
[6]: https://ext4.wiki.kernel.org/index.php/Main_Page
[7]: https://man7.org/linux/man-pages/man8/lvm.8.html
[8]: https://fedoraproject.org/wiki/Changes/BtrfsByDefault
[9]: https://man7.org/linux/man-pages/man5/filesystems.5.html
[10]: https://docs.fedoraproject.org/en-US/Fedora/11/html/Release_Notes/index.html#sect-Release_Notes-Fedora_11_Overview
[11]: https://facebookmicrosites.github.io/btrfs/docs/btrfs-facebook.html
[12]: https://www.suse.com/releasenotes/x86_64/SUSE-SLES/12/#fate-317221
[13]: https://fedoramagazine.org/wp-content/uploads/2020/12/ext4-on-LVM.jpg
[14]: https://opensource.com/article/18/4/ext4-filesystem
[15]: https://man7.org/linux/man-pages/man8/e4defrag.8.html
[16]: https://libvirt.org/storage.html#StorageBackendLogical
[17]: https://www.redhat.com/sysadmin/create-volume-group
[18]: https://www.redhat.com/sysadmin/create-physical-volume
[19]: https://tldp.org/HOWTO/LVM-HOWTO/snapshotintro.html
[20]: https://man7.org/linux/man-pages/man7/lvmthin.7.html
[21]: https://rhea.dev/articles/2018-08/LVM-RAID-on-Fedora
[22]: https://en.wikipedia.org/wiki/Standard_RAID_levels#RAID_0
[23]: https://en.wikipedia.org/wiki/Standard_RAID_levels#RAID_1
[24]: https://en.wikipedia.org/wiki/Standard_RAID_levels#RAID_5
[25]: https://en.wikipedia.org/wiki/Standard_RAID_levels#RAID_6
[26]: https://en.wikipedia.org/wiki/Non-standard_RAID_levels#Linux_MD_RAID_10
[27]: https://man7.org/linux/man-pages/man8/dmsetup.8.html
[28]: https://man7.org/linux/man-pages/man4/md.4.html
[29]: https://fedoramagazine.org/managing-raid-arrays-with-mdadm/
[30]: https://man7.org/linux/man-pages/man7/lvmcache.7.html
[31]: https://fedoramagazine.org/wp-content/uploads/2020/12/Btrfs-Volume.jpg
[32]: https://en.wikipedia.org/wiki/ZFS
[33]: https://itsfoss.com/linus-torvalds-zfs/
[34]: https://btrfs.wiki.kernel.org/index.php/FAQ#Can_I_have_nodatacow_.28or_chattr_.2BC.29_but_still_have_checksumming.3F
[35]: https://arstechnica.com/information-technology/2014/01/bitrot-and-atomic-cows-inside-next-gen-filesystems/
[36]: https://man7.org/linux/man-pages/man8/mkfs.btrfs.8.html#DUP_PROFILES_ON_A_SINGLE_DEVICE
[37]: https://en.wikipedia.org/wiki/Copy-on-write
[38]: https://btrfs.wiki.kernel.org/index.php/Deduplication
[39]: https://btrfs.wiki.kernel.org/index.php/UseCases#How_do_I_copy_a_large_file_and_utilize_COW_to_keep_it_from_actually_being_copied.3F
[40]: https://fedoramagazine.org/btrfs-snapshots-backup-incremental/
[41]: http://snapper.io/
[42]: https://btrfs.wiki.kernel.org/index.php/Compression
[43]: https://www.man7.org/linux/man-pages/man1/chattr.1.html
[44]: https://btrfs.wiki.kernel.org/index.php/Conversion_from_Ext3
[45]: https://fedoramagazine.org/reclaim-hard-drive-space-with-lvm/