3.9 File Systems and Storage

Oracle Linux 8 introduces the following notable file systems and storage features, enhancements, and changes:

  • Btrfs file system removed in RHCK.  The Btrfs file system is removed from RHCK in Oracle Linux 8. As such, you cannot create or mount Btrfs file systems when using this kernel. Also, no Btrfs user-space packages are provided in this release. If you are using Btrfs, continue to use Oracle Linux 7.

  • OCFS2 file system support not available in RHCK.  The OCFS2 file system is not supported on RHCK in Oracle Linux 8. If you need to use OCFS2, continue to run Oracle Linux 7.

  • NFSv3 over UDP support not available in Oracle Linux 8.  In Oracle Linux 8, by default, the NFS server no longer opens or listens on a User Datagram Protocol (UDP) socket. Note that this change impacts NFS version 3 (NFSv3) only, as version 4 requires the Transmission Control Protocol (TCP).

  • DM Multipathing enhancements.  Oracle Linux 8 introduces some noteworthy enhancements for the Device Mapper Multipathing (DM Multipathing) configuration, including the following:

    • New overrides section has been added to the /etc/multipath.conf file. You can enter a configuration value for all of your devices by using this section. The attributes that you set are then used by DM Multipathing for all of your devices, unless the values are overwritten by any attributes that are set in the multipaths section of the /etc/multipath.conf file for paths that contain the device. Note that this new functionality is a replacement for the all_devs parameter in the devices section of the configuration file, which is no longer supported.

    • Support for improved detection of marginal paths has been added to the multipathd service. This enhancement helps multipath devices avoid paths that are likely to fail repeatedly, thereby improving performance. For more details about this change, including information about the options in the /etc/multipath.conf file that control marginal paths behavior, see the multipath.conf man page.

  • SCSI Multiqueue driver support added.  In Oracle Linux 8, block devices use multiqueue scheduling. This feature enhancement enables block layer performance to scale well with fast solid-state drives (SSDs) and multi-core systems.

    Also, the SCSI Multiqueue (scsi-mq) driver is enabled by default and the kernel boots with the scsi_mod.use_blk_mq=Y option. Note that a requirement of DM Multipathing is that the scsi-mq driver be active.

  • Stratis local storage manager introduced.  Oracle Linux 8 includes the Stratis local storage management tool. Stratis enables you to perform complex storage tasks and manage your storage stack more easily by using a unified interface.

  • XFS support for shared COW data extents.  The XFS file system now supports shared copy-on-write (COW) data extent functionality, whereby two or more files can share a common set of data blocks. This feature is similar to Copy on write (COW) functionality that is found in other file systems, where if either of the files that are sharing common blocks change, XFS breaks the link to those common blocks and then creates a new file.

    Shared COW extents are fast, space efficient, and transparent. User-space utilities can use COW extents for cloning, per-file snapshots, and out-of-band deduplication. Some kernel subsystems, such as Overlayfs and NFS, also use COW extents.

    Shared COW data extents are currently disabled by default during the creation of an XFS file system, in the xfsprogs 4.19.0-2.0.1.el8 package version. To create an XFS file system with this feature enabled, run the following command:

    # mkfs.xfs -m crc=1,reflink=1 block-device

    Future versions of xfsprogs are likely to enable this functionality by default.

  • Technology Preview: Clustered Bitmap on MD Raid.  The mdadm command, used to manage MD Raid devices, includes the --bitmap=clustered option to store the bitmap for the array within a clustered environment. This feature is available as a technology preview and is unsupported on Oracle Linux 8.