If you use the --alloc-start option with mkfs.btrfs to specify an offset for the start of the file system, the size of the file system should be smaller but this is not the case. It is also possible to specify an offset that is higher than the device size. (Bug ID 16946255)

The usage information for mkfs.btrfs reports raid5 and raid6 as possible profiles for both data and metadata. However, the kernel does not support these features and cannot mount file systems that use them. (Bug ID 16946303)

The btrfs filesystem balance command does not warn that the RAID level can be changed under certain circumstances, and does not provide the choice of cancelling the operation. (Bug ID 16472824)

Converting an existing ext2, ext3, or ext4 root file system to btrfs does not carry over the associated security contexts that are stored as part of a file's extended attributes. With SELinux enabled and set to enforcing mode, you might experience many permission denied errors after reboot, and the system might be unbootable. To avoid this problem, enforce automatic file system relabeling to run at bootup time. To trigger automatic relabeling, create an empty file named .autorelabel (for example, by using touch) in the file system's root directory before rebooting the system after the initial conversion. The presence of this file instruct SELinux to recreate the security attributes for all files on the file system. If you forget to do this and rebooting fails, either temporarily disable SELinux completely by adding selinux=0 to the kernel boot parameters, or disable enforcing of the SELinux policy by adding enforcing=0. (Bug ID 13806043)

Commands such as du can show inconsistent results for file sizes in a btrfs file system when the number of bytes that is under delayed allocation is changing. (Bug ID 13096268)

The copy-on-write nature of btrfs means that every operation on the file system initially requires disk space. It is possible that you cannot execute any operation on a disk that has no space left; even removing a file might not be possible. The workaround is to run sync before retrying the operation. If this does not help, remount the file system with the -o nodatacow option and delete some files to free up space. See https://btrfs.wiki.kernel.org/index.php/ENOSPC.

Btrfs has a limit of 237 or fewer hard links to a file from a single directory. The exact limit depends on the number of characters in the file name. The limit is 237 for a file with up to eight characters in its file name; the limit is lower for longer file names. Attempting to create more than this number of links results in the error Too many links. You can create more hard links to the same file from another directory. Although the limitation of the number of hard links in a single directory has been increased to 65535, the version of mkfs.btrfs that is provided in the btrfs-progs package does not yet support the compatibility flag for this feature. (Bug ID 16285431)

If you run the btrfs quota enable command on a non-empty file system, any existing files do not count toward space usage. Removing these files can cause usage reports to display negative numbers and the file system to be inaccessible. The workaround is to enable quotas immediately after creating the file system. If you have already written data to the file system, it is too late to enable quotas. (Bug ID 16569350)

The btrfs quota rescan command is not currently implemented. The command does not perform a rescan and returns without displaying any message. (Bug ID 16569350)

When you overwrite data in a file, starting somewhere in the middle of the file, the overwritten space is counted twice in the space usage numbers that btrfs qgroup show displays. (Bug ID 16609467)

If you run btrfsck --init-csum-tree on a file system and then run a simple btrfsck on the same file system, the command displays a Backref mismatch error that was not previously present. (Bug ID 16972799)

If you use the -s option to specify a sector size to mkfs.btrfs that is different from the page size, the created file system cannot be mounted. By default, the sector size is set to be the same as the page size. (Bug ID 17087232)

The btrfs subvolume delete command may result in a "Directory not empty" error. This error message is incorrect. The actual reason that the subvolume cannot be deleted is that the subvolume is configured as the default subvolume. The default subvolume is the subvolume that is mounted when no subvolume is specified with the mount command. Before you can delete the subvolume, you need to configure a different default subvolume using the btrfs subvolume set-default command. (Bug ID 17661944)

Defragmentation can break data block sharing. Due to the copy-on-write design of btrfs, snapshots initially share the same data blocks of the original subvolume. However, when either the snapshot or the subvolume is defragmented, this sharing can be undone, resulting in a higher disk space usage.

Using kill -9 to terminate dtrace can leave breakpoints outstanding in processes being traced, which might sooner or later kill them.

Argument declarations for probe definitions cannot be declared with derived types such as enum, struct, or union.

The following compiler warning can be ignored for probe definition arguments of type string (which is a D type but not a C type):

provider_def.h:line#: warning: parameter names (without types) in function declaration

HVM guests

PV guests

Oracle Database

You might see the following warning messages if you use the ibportstate disable command to disable a switch port:

ibwarn: [2696] _do_madrpc: recv failed: Connection timed out
ibwarn: [2696] mad_rpc: _do_madrpc failed; dport (Lid 38)
ibportstate: iberror: failed: smp set portinfo failed

You can safely ignore these warnings. (Bug ID 16248314)

The Internet Protocol over InfiniBand (IPoIB) driver supports the use of either connected mode or datagram mode with an interface, where datagram mode is the default mode. Changing the mode of an InfiniBand interface by echoing either connected or datagram to /sys/class/net/ibN/mode is not supported. It is also not possible to change the mode of an InfiniBand interface while it is enabled.

To change the IPoIB mode of an InfiniBand interface:

(Bug ID 17479833)

When the rds_ib_srq parameter for the rds_rdma module is enabled and the module is in use (for example when running the rds-stress tool), restarting the rdma service (which reloads the rds_rdma module) generates error messages visible in dmesg or /var/log/messages. (Bug ID 18243427)

The correct operation of containers might require that you completely disable SELinux on the host system. For example, SELinux can interfere with container operation under the following conditions:

To disable SELinux on the host:

The root user in a container can affect the configuration of the host system by setting some /proc entries. (Bug ID 17190287)

Using yum to update packages inside the container that use init scripts can undo changes made by the Oracle template.

Migrating live containers (lxc-checkpoint) is not yet supported.

Oracle Database is not yet supported for use with Linux Containers. The following information is intended for those who want to experiment with such a configuration.

The following /proc parameter files may only be set on the host and not for individual containers:

Setting the parameters in the host to the Oracle recommended values sets them for all containers and allows the Oracle database to run in a container. For more information, see Configuring Kernel Parameters and Resource Limits. (Bug ID 17217854)

If a Device or resource busy - failed to set memory.use_hierarchy to 1 error message is displayed when you start a container, edit the /etc/cgconfig.conf file and add the following:

group . {
memory {
memory.use_hierarchy = "1";
}
}

(Bug ID 19237222)

When booting UEK R3 as a PVHVM guest, you can safely ignore the following kernel message:

register_vcpu_info failed:
          err=-38

(Bug ID 13713774)

Under Oracle VM Server 3.1.1, migrating a PVHVM guest that is running the UEK R3 kernel causes a disparity between the date and time as displayed by date and hwclock. To prevent this from occurring, upgrade to Oracle VM Server 3.2.1 or later. The workaround post migration is either to run the command hwclock --hctosys on the guest or to reboot the guest. (Bug ID 16861041)

On virtualized systems that are built on Xen version 3, including all releases of Oracle VM 2 including 2.2.2 and 2.2.3, disk synchronization requests for ext3 and ext4 file systems result in journal corruption with kernel messages similar to the following being logged:

blkfront: barrier: empty write xvda op failed
blkfront: xvda: barrier or flush: disabled

In addition, journal failures such as the following might be reported:

Aborting journal on device xvda1

The workaround is to add the mount option barrier=0 to all ext3 and ext4 file systems in the guest VM before upgrading to UEK R3. For example, you would change a mount entry such as:

UUID=4e4287b1-87dc-47a8-b69a-075c7579eaf1  /  ext3  defaults  1 1

so that it reads:

UUID=4e4287b1-87dc-47a8-b69a-075c7579eaf1  /  ext3  defaults,barrier=0  1 1

This issue does not apply to Xen 4 based systems, such as Oracle VM 3. (Bug ID 17310816)

In some circumstances, xfsdump can fail when the file system to be backed up is specified as a mount point, for example:

xfsdump: ERROR: /mnt/myxfs/ does not identify a file system

The workaround is to specify the file system by its device name, for example /dev/sdb. (Bug ID 18483275)

In a virtual machine, the intensive direct I/O on files which are being fragmented by fallocate and punch_hole in parallel may result, in some circumstances, in data corruption with the error Invalid or incomplete multibyte or wide character. (Bug ID 18711409)

The following message might be displayed when you use the xfs_growfs command:

 xfs_growfs: cannot find mount point for path `mount_point': Success 

The message is caused by an incorrect mounted project path listed in the XFS project quota initialization file, /etc/projects. If you are not using project quotas, remove the /etc/projects file. (Bug ID 18886520)