Chapter 12. File systems and storage
12.1. File systems
12.1.1. Btrfs has been removed
The Btrfs file system has been removed in Red Hat Enterprise Linux 8. This includes the following components:
You can no longer create, mount, or install on Btrfs file systems in Red Hat Enterprise Linux 8. The Anaconda installer and the Kickstart commands no longer support Btrfs.
12.1.2. XFS now supports shared copy-on-write data extents
The XFS file system supports shared copy-on-write data extent functionality. This feature enables two or more files to share a common set of data blocks. When either of the files sharing common blocks changes, XFS breaks the link to common blocks and creates a new file. This is similar to the copy-on-write (COW) functionality found in other file systems.
Shared copy-on-write data extents are:
- Creating shared copies does not utilize disk I/O.
- Shared blocks do not consume additional disk space.
- Files sharing common blocks act like regular files.
Userspace utilities can use shared copy-on-write data extents for:
Efficient file cloning, such as with the
- Per-file snapshots
This functionality is also used by kernel subsystems such as Overlayfs and NFS for more efficient operation.
Shared copy-on-write data extents are now enabled by default when creating an XFS file system, starting with the
xfsprogs package version
Note that Direct Access (DAX) devices currently do not support XFS with shared copy-on-write data extents. To create an XFS file system without this feature, use the following command:
# mkfs.xfs -m reflink=0 block-device
Red Hat Enterprise Linux 7 can mount XFS file systems with shared copy-on-write data extents only in the read-only mode.
12.1.3. The ext4 file system now supports metadata checksums
With this update, ext4 metadata is protected by checksums. This enables the file system to recognize the corrupt metadata, which avoids damage and increases the file system resilience.
/etc/sysconfig/nfs file and legacy NFS service names are no longer available
In Red Hat Enterprise Linux 8.0, the NFS configuration has moved from the
/etc/sysconfig/nfs configuration file, which was used in Red Hat Enterprise Linux 7, to
/etc/nfs.conf file uses a different syntax. Red Hat Enterprise Linux 8 attempts to automatically convert all options from
/etc/nfs.conf when upgrading from Red Hat Enterprise Linux 7.
Both configuration files are supported in Red Hat Enterprise Linux 7. Red Hat recommends that you use the new
/etc/nfs.conf file to make NFS configuration in all versions of Red Hat Enterprise Linux compatible with automated configuration systems.
Additionally, the following NFS service aliases have been removed and replaced by their upstream names:
nfs.service, replaced by
nfs-secure.service, replaced by
rpcgssd.service, replaced by
nfs-idmap.service, replaced by
rpcidmapd.service, replaced by
nfs-lock.service, replaced by
nfslock.service, replaced by
12.2.1. The BOOM boot manager simplifies the process of creating boot entries
BOOM is a boot manager for Linux systems that use boot loaders supporting the BootLoader Specification for boot entry configuration. It enables flexible boot configuration and simplifies the creation of new or modified boot entries: for example, to boot snapshot images of the system created using LVM.
BOOM does not modify the existing boot loader configuration, and only inserts additional entries. The existing configuration is maintained, and any distribution integration, such as kernel installation and update scripts, continue to function as before.
BOOM has a simplified command-line interface (CLI) and API that ease the task of creating boot entries.
12.2.2. Stratis is now available
Stratis is a new local storage manager. It provides managed file systems on top of pools of storage with additional features to the user.
Stratis enables you to more easily perform storage tasks such as:
- Manage snapshots and thin provisioning
- Automatically grow file system sizes as needed
- Maintain file systems
To administer Stratis storage, use the
stratis utility, which communicates with the
stratisd background service.
Stratis is provided as a Technology Preview.
For more information, see the Stratis documentation: Setting up Stratis file systems.
12.2.3. LUKS2 is now the default format for encrypting volumes
In RHEL 8, the LUKS version 2 (LUKS2) format replaces the legacy LUKS (LUKS1) format. The
dm-crypt subsystem and the
cryptsetup tool now uses LUKS2 as the default format for encrypted volumes. LUKS2 provides encrypted volumes with metadata redundancy and auto-recovery in case of a partial metadata corruption event.
Due to the internal flexible layout, LUKS2 is also an enabler of future features. It supports auto-unlocking through the generic kernel-keyring token built in
libcryptsetup that allow users unlocking of LUKS2 volumes using a passphrase stored in the kernel-keyring retention service.
Other notable enhancements include:
- The protected key setup using the wrapped key cipher scheme.
- Easier integration with Policy-Based Decryption (Clevis).
- Up to 32 key slots - LUKS1 provides only 8 key slots.
For more details, see the
cryptsetup-reencrypt(8) man pages.
12.2.4. Multiqueue scheduling on block devices
Block devices now use multiqueue scheduling in Red Hat Enterprise Linux 8. This enables the block layer performance to scale well with fast solid-state drives (SSDs) and multi-core systems.
The SCSI Multiqueue (
scsi-mq) driver is now enabled by default, and the kernel boots with the
scsi_mod.use_blk_mq=Y option. This change is consistent with the upstream Linux kernel.
Device Mapper Multipath (DM Multipath) requires the
scsi-mq driver to be active.
12.2.5. VDO now supports all architectures
Virtual Data Optimizer (VDO) is now available on all of the architectures supported by RHEL 8.
12.2.6. VDO no longer supports read cache
The read cache functionality has been removed from Virtual Data Optimizer (VDO). The read cache is always disabled on VDO volumes, and you can no longer enable it using the
--readCache option of the
Red Hat might reintroduce the VDO read cache in a later Red Hat Enterprise Linux release, using a different implementation.
dmraid package has been removed
dmraid package has been removed from Red Hat Enterprise Linux 8. Users requiring support for combined hardware and software RAID host bus adapters (HBA) should use the
mdadm utility, which supports native MD software RAID, the SNIA RAID Common Disk Data Format (DDF), and the Intel® Matrix Storage Manager (IMSM) formats.
12.2.8. Software FCoE and Fibre Channel no longer support the target mode
- Software FCoE: NIC Software FCoE target functionality is removed in Red Hat Enterprise Linux 8.0.
Fibre Channel no longer supports the target mode. Target mode is disabled for the
qla2xxxQLogic Fibre Channel driver in Red Hat Enterprise Linux 8.0.
For more information, see FCoE software removal.
12.2.9. The detection of marginal paths in DM Multipath has been improved
multipathd service now supports improved detection of marginal paths. This helps multipath devices avoid paths that are likely to fail repeatedly, and improves performance. Marginal paths are paths with persistent but intermittent I/O errors.
The following options in the
/etc/multipath.conf file control marginal paths behavior:
DM Multipath disables a path and tests it with repeated I/O for the configured sample time if:
multipath.confoptions are set,
- a path fails twice in the configured time, and
- other paths are available.
If the path has more than the configured err rate during this testing, DM Multipath ignores it for the configured gap time, and then retests it to see if it is working well enough to be reinstated.
For more information, see the
multipath.conf man page.
overrides section of the DM Multipath configuration file
/etc/multipath.conf file now includes an
overrides section that allows you to set a configuration value for all of your devices. These attributes are used by DM Multipath for all devices unless they are overwritten by the attributes specified in the
multipaths section of the
/etc/multipath.conf file for paths that contain the device. This functionality replaces the
all_devs parameter of the
devices section of the configuration file, which is no longer supported.
12.2.11. NVMe/FC is fully supported on Broadcom Emulex and Marvell Qlogic Fibre Channel adapters
The NVMe over Fibre Channel (NVMe/FC) transport type is now fully supported in Initiator mode when used with Broadcom Emulex and Marvell Qlogic Fibre Channel 32Gbit adapters that feature NVMe support.
NVMe over Fibre Channel is an additional fabric transport type for the Nonvolatile Memory Express (NVMe) protocol, in addition to the Remote Direct Memory Access (RDMA) protocol that was previously introduced in Red Hat Enterprise Linux.
To enable NVMe/FC in the
lpfcdriver, edit the
/etc/modprobe.d/lpfc.conffile and add the following option:
To enable NVMe/FC in the
qla2xxxdriver, edit the
/etc/modprobe.d/qla2xxx.conffile and add the following option:
- NVMe clustering is not supported with NVMe/FC.
kdumpis not supported with NVMe/FC.
- Booting from Storage Area Network (SAN) NVMe/FC is not supported.
12.2.12. Support for Data Integrity Field/Data Integrity Extension (DIF/DIX)
DIF/DIX is an addition to the SCSI Standard. It remains in Technology Preview for all HBAs and storage arrays, except for those specifically listed as supported.
DIF/DIX increases the size of the commonly used 512 byte disk block from 512 to 520 bytes, adding the Data Integrity Field (DIF). The DIF stores a checksum value for the data block that is calculated by the Host Bus Adapter (HBA) when a write occurs. The storage device then confirms the checksum on receipt, and stores both the data and the checksum. Conversely, when a read occurs, the checksum can be verified by the storage device, and by the receiving HBA.
libstoragemgmt-netapp-plugin has been removed
libstoragemgmt-netapp-plugin package used by the
libStorageMgmt library has been removed. It is no longer supported because:
- The package requires the NetApp 7-mode API, which is being phased out by NetApp.
RHEL 8 has removed default support for the TLSv1.0 protocol with the
TLS_RSA_WITH_3DES_EDE_CBC_SHAcipher, using this plug-in with TLS does not work.
12.2.14. Removal of Cylinder-Head-Sector addressing from
Cylinder-Head-Sector (CHS) addressing is no longer useful for modern storage devices. It has been removed as an option from the
cfdisk commands. Since RHEL 8, you cannot use the following options:
-C, --cylinders number
-H, --heads number
-S, --sectors number
For more information, see the
cfdisk(8) man pages.
12.3.1. Removal of
clvmd for managing shared storage devices
LVM no longer uses
clvmd (cluster lvm daemon) for managing shared storage devices. Instead, LVM now uses
lvmlockd (lvm lock daemon).
For details about using
lvmlockd, see the
lvmlockd(8)man page. For details about using shared storage in general, see the
For information about using LVM in a Pacemaker cluster, see the help screen for the
- For an example of a procedure to configure a shared logical volume in a Red Hat High Availability cluster, see Configuring a GFS2 file system in a cluster.
12.3.2. Removal of
LVM no longer uses the
lvmetad daemon for caching metadata, and will always read metadata from disk. LVM disk reading has been reduced, which reduces the benefits of caching.
Previously, autoactivation of logical volumes was indirectly tied to the
use_lvmetad setting in the
lvm.conf configuration file. The correct way to disable autoactivation continues to be setting
auto_activation_volume_list in the
12.3.3. LVM can no longer manage devices formatted with the GFS pool volume manager or the
lvm1 metadata format.
LVM can no longer manage devices formatted with the GFS pool volume manager or the`lvm1` metadata format. if you created your logical volume before Red Hat Enterprise Linux 4 was introduced, then this may affect you. Volume groups using the
lvm1 format should be converted to the
lvm2 format using the
12.3.4. LVM libraries and LVM Python bindings have been removed
lvm2app library and LVM Python bindings, which were provided by the
lvm2-python-libs package, have been removed. Red Hat recommends the following solutions instead:
The LVM D-Bus API in combination with the
lvm2-dbusdservice. This requires using Python version 3.
The LVM command-line utilities with JSON formatting; this formatting has been available since the
lvm2package version 2.02.158.
libblockdevlibrary, included in AppStream, for C/C++
You must port any applications using the removed libraries and bindings to the D-Bus API before upgrading to Red Hat Enterprise Linux 8.
12.3.5. The ability to mirror the log for LVM mirrors has been removed
The mirrored log feature of mirrored LVM volumes has been removed. Red Hat Enterprise Linux (RHEL) 8 no longer supports creating or activating LVM volumes with a mirrored mirror log.
The recommended replacements are:
- RAID1 LVM volumes. The main advantage of RAID1 volumes is their ability to work even in degraded mode and to recover after a transient failure.
Disk mirror log. To convert a mirrored mirror log to disk mirror log, use the following command:
lvconvert --mirrorlog disk my_vg/my_lv.