To avoid unnecessary confusion, this is more intended for Linux distributions, kernel developers and maintainers rather than individual Linux users. ZFS was open sourced around This would have meant that Linux distributions start supporting ZFS. These two open source licenses are not fully compatible with each other. While the whole derivative thing is a matter of debate for legal and licensing experts, Torvalds is skeptical of Oracle.
Oracle has a history of suing enterprises for using its code. Remember Oracle vs Android lawsuit over the use of Java? If somebody adds a kernel module like ZFS, they are on their own.
So they took their chances and now they provide an option to use ZFS on root from Ubuntu It is also possible to rollback the live system to a previous snapshot. All changes made since the snapshot will be lost. Whenever new data is written to ZFS, it creates a checksum for that data. When that data is read, the checksum is verified. If the checksum does not match, then ZFS knows that an error has been detected. ZFS will then automatically attempt to correct the error.
RAID-Z2 required at least two storage drives and two drive for parity. RAID-Z3 requires at least two storage drives and three drive for parity. When ZFS was created, it was designed to be the last word in file systems. At a time when most file systems where bit, the ZFS creators decided to jump right to bit to future proof it. If you want to try ZFS on Linux, you can use it as your storage file system.
Recently, Ubuntu Read more about using ZFS on Ubuntu. This article has sung the benefits of ZFS. Now let me tell you a quick problem with ZFS.
Using RAID-Z can be expensive because of the number of drives you need to purchase to add storage space. If you found this article interesting, please take a minute to share it on social media, Hacker News or Reddit. My name is John Paul Wohlscheid. I'm an aspiring mystery writer who loves to play with technology, especially Linux.
You can catch up with me at my personal website. You can check out my ebooks here. I just went through a night mare with LVM2 shared from a Linux server to mac books. It would not create the full size of the entire storage pool i.
I installed ZFS and configuration was a snap, the entire 7TB was configure without a problem and performance surpasswd LVM2 by copying the same amount of data in just 10 minutes. The basic storage elements are single devices, mirrors and raidz. All of these storage elements are called vdevs. Mirrored vdevs in a zpool present storage that's the size of the smallest physical drive. A mirrored vdev can be upgraded that is, increased in size by attaching larger drives to the mirrorset and "resilvering" synchronizing the mirrors , then detaching the smaller drives from the set Resilvering a mirror will involve copying only used blocks to the target device—unused blocks are not touched, which can make resilvering much faster than hardware-maintained disk mirroring which copies unused storage.
ZFS also can maintain RAID devices, and unlike most storage controllers, it can do so without battery-backed cache as long as the physical drives honor "write barriers".
ZFS can create a raidz vdev with multiple levels of redundancy, allowing the failure of up to three physical drives while maintaining array availability. Resilvering a raidz also involves only used blocks and can be much faster than a storage controller that copies all disk blocks during a RAID rebuild. A raidz vdev should normally compose 8—12 drives larger raidz vdevs are not recommended. Note that the number of drives in a raidz cannot be expanded. ZFS greatly prefers to manage raw disks.
ZFS is able to enforce storage integrity far better than any RAID controller, as it has intimate knowledge of the structure of the filesystem. Data safety is an important design feature of ZFS. All blocks written in a zpool are aggressively checksummed to ensure the data's consistency and correctness.
You can select the checksum algorithm from sha, fletcher2 or fletcher4. You can change the checksum algorithm at any time, and new blocks will use the updated algorithm. A checksum is stored separately from the data block, with the parent block, in the hope that localized block damage can be detected.
ZFS can implement "deduplication" by maintaining a searchable index of block checksums and their locations. If a new block to be written matches an existing block within the index, the existing block is used instead, and space is saved.
In this way, multiple files may share content by maintaining single copies of common blocks, from which they will diverge if any of their content changes. The documentation states that a "dedup-capable checksum" must be set before dedup can be enabled, and sha is offered as an example—the checksum must be "collision-resistant" to identify a block uniquely to assure the safety of dedup.
Be warned that memory requirements for ZFS expand drastically when deduplication is enabled, which quickly can overwhelm a system lacking sufficient resources. The zpool can hold datasets, snapshots, clones and volumes. A "dataset" is a standard ZFS filesystem that has a mountpoint and can be modified. A "snapshot" is a point-in-time copy of a filesystem, and as the parent dataset is changed, the snapshot will collect the original blocks to maintain a consistent past image.
A "clone" can be built upon a snapshot and allows a different set of changes to be applied to the past image, effectively allowing a filesystem to branch—the clone and original dataset will continue to share unchanged blocks, but otherwise will diverge.
A "volume" is similar to a block device, and can be loopback-mounted with a filesystem of any type, or perhaps presented as an iscsi target. Checksums are enforced on volumes. Note that, unlike partitions or logical volumes, elements in a zpool can be intermingled. ZFS knows that the outside edge of a disk is faster than the interior, and it may decide to mix blocks from multiple objects in a zpool at these locations to increase performance. Due to this commingling of filesystems, forensic analysis of zpools is difficult and expensive:.
But, no matter how much searching you do, there is [sic] no ZFS recovery tools out there. You are welcome to call companies like Ontrack for data recovery.
There are no fsck or defrag tools for ZFS datasets. The boot process never will be delayed because a dataset was not cleanly unmounted. There is a "scrub" tool that will walk a dataset and verify the checksum of every used block on all vdevs, but the scrub takes place on mounted and active datasets.
ZFS can recover very well from power losses or otherwise dirty dismounts. Fragmentation in ZFS is a larger question, and it appears related more to remaining storage capacity than rapid file growth and reduction. It is important to provide ample free disk space to datasets that will see heavy use. Error-correcting memory is advised as critical for the correct processing of checksums that maintain zpool consistency.
ECC memory is normally found in servers, but becomes somewhat rare with desktops and laptops. FUSE is an interface that allows a filesystem to be implemented by a process that runs in userspace. Fedora has maintained zfs-fuse as an RPM package for some time, but this package does not appear in any of the Red Hat-based distributions, including Oracle Linux.
The zfs-fuse implementation is likely reasonable for local, archival and potentially compressed datasets. Some have used Btrfs for ad-hoc compressed filesystems , and zfs-fuse is certainly an option for similar activity. The last version of zfs-fuse that will work in Oracle Linux 7. The zfs-fuse userspace agent must be executed before any zpools can be manipulated note a systemd unit is included for this purpose :. It is usually most convenient to dedicate an entire disk to a zpool, so delete all the existing partitions:.
Now a zpool can be added on the drive note that creating a pool adds a dataset of the same name, which, as you see here, is automatically mounted :.
Creating a zpool on non-redundant devices is informally known as "hating your data" and should be contemplated only for demonstration purposes. However, zpools on non-redundant media for example, flash drives have obvious data-consistency and compression advantages to VFAT, and the copies parameter can be adjusted for such a dataset to force all blocks to be recorded on the media multiple times up to three to increase recoverability.
Additional drives can be added as mirrors to an existing drive with zpool attach. Creating an additional dataset and mounting it is as easy as creating a directory note this command can take some time :. ZFS supports several types of compression in a dataset. Gzip of varying degrees, zle and lzjb can all be present in a single mountpoint.
The checksum algorithm also can be adjusted on the fly:. This will directly impact the speed and responsiveness of a dataset:. Normally, snapshots are visible in the.
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