ZFS compression

Alejandro is a Storage and Filesystems Manager at Red Hat. One department at Red Hat wants to move all of their servers to the ZFS filesytem, and to compress all old archived files and folders. Please teach Alejandro the following about ZFS (Note that Alejandro prefers the term "Free Software" to "open-source"):

  1. What is ZFS?
  2. What is the history of ZFS?
  3. What are the strengths and weakneses of ZFS?
  4. How can ZFS be implemented using Free Software?
  5. How would one compress files and folders using ZFS on RHEL GNU/Linux servers?

What is ZFS?

ZFS, which stands for Zettabyte File System, is an advanced file system and logical volume manager designed to overcome many of the major problems found in previous file systems and volume managers. It provides powerful features such as high storage capacity, protection against data corruption, support for high storage capacities, efficient data compression, snapshots, and copy-on-write clones, continuous integrity checking and automatic repair, and RAID-Z.

History of ZFS

ZFS was originally developed by Sun Microsystems for the Solaris Operating System and released in 2005. After Oracle acquired Sun in 2010, the original ZFS project became closed source. However, the last version released under Sun was already under the CDDL (Common Development and Distribution License), a type of free software license, which allowed the community to continue developing it.

This resulted in the creation of OpenZFS, which is the truly free software and community-supported version of ZFS. OpenZFS has been ported to various Unix-like systems, including FreeBSD and Linux, and has been incorporated into several free software projects.

Strengths of ZFS

  1. Data Integrity: ZFS uses a model that ensures data is verified using a checksum and repaired on the fly if corrupted.
  2. Scalability: ZFS can handle very large amounts of storage.
  3. Snapshots and Clones: These are used for backing up and for the efficient creation of duplicate datasets and virtual machine disks.
  4. Dynamic Striping: ZFS stripes data across all available disks which can improve performance.
  5. Built-in RAID: ZFS offers RAID-Z which is a more flexible and reliable alternative to traditional RAID setups.
  6. Copy-on-write: This feature allows for more efficient disk writes and data protection.
  7. Compression: ZFS supports on-the-fly compression which can be highly beneficial for archival storage.

Weaknesses of ZFS

  1. Memory Usage: ZFS is known for its high memory requirements, especially the ARC (Adaptive Replacement Cache).
  2. License Compatibility: The CDDL is not compatible with the GNU General Public License (GPL), which can limit its integration with systems that are strictly GPL.
  3. Complexity: Managing ZFS and understanding its features can be complex for new users.
  4. Performance: Certain workloads, especially on systems with limited resources, may experience performance degradation.

Implementing ZFS using Free Software

On Red Hat Enterprise Linux (RHEL) and similar GNU/Linux systems, ZFS is available through the OpenZFS project. To implement ZFS, one would typically need to install the ZFS kernel modules and userland tools, which are not included in the RHEL package repositories due to license incompatibilities. These can be obtained from the ZFS on Linux project, which is now part of OpenZFS.

Here are the general steps to implement ZFS on a RHEL GNU/Linux server:

  1. Add the ZFS repository: The repository information is provided by the OpenZFS project.
  2. Install ZFS: Using the package manager, install the ZFS packages.
  3. Load the ZFS kernel module: Ensure that the ZFS kernel module is loaded into the system.
  4. Create ZFS pools and file systems: Use zpool to create storage pools and zfs to create file systems.
  5. Configure ZFS settings: Adjust ZFS settings as needed, including setting up compression, if desired.

Compressing Files and Folders using ZFS

On a ZFS file system, compression is a property that can be enabled or changed at any time without downtime. To enable or adjust compression on an existing ZFS dataset, you would use the zfs command.

Here is an example of how to enable compression on a dataset:

zfs set compression=on poolname/datasetname

You can also choose a specific compression algorithm, like LZ4 (recommended for its performance and compression ratio):

zfs set compression=lz4 poolname/datasetname

To compress all old archived files and folders, you would set the compression on the datasets containing these files. ZFS will compress files as they are written, so for files that are already on the disk, you'd need to copy them or rewrite them to the disk for compression to take effect.

Here is how you could force the compression of existing files:

  1. Enable compression on the dataset.
  2. Use the zfs send and zfs receive to rewrite the data to the same or a new dataset, which will apply compression.

It's important to note that enabling compression on a busy production system should be done with caution and preferably during a maintenance window, as it can increase CPU utilization. However, ZFS compression is generally very efficient and can often lead to performance improvements due to reduced disk I/O.

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