• 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)

• 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.

• 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. Using the btrfs quota rescan does not help fix this issue either. (Bug ID 16609467)

• 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-progs and btrfs-progs-devel packages for use with UEK R4 are made available in the ol6_x86_64_UEKR4 and ol7_x86_64_UEKR4 ULN channels and the ol6_UEKR4 and ol7_UEKR4 Oracle Linux yum server repositories. In UEK R3, these packages were made available in the ol6_x86_64_latest and ol7_x86_64_latest ULN channels and the ol6_latest and ol7_latest Oracle Linux yum server repositories.

The Data Integrity Field (DIF) and Data Integrity Extension (DIX) features that have been added to the SCSI standard are dependent on a file system that is capable of correctly handling attempts by the memory management system to change data in the buffer while it is queued for a write.

The ext2, ext3 and ext4 file system drivers do not prevent pages from being modified during I/O which can cause checksum failures and a "Logical block guard check failed" error. Other file systems such as XFS are supported. (Bug ID 24361968)

• Running yum install within a container on an overlayfs file system can fail with the following error:

  Rpmdb checksum is invalid: dCDPT(pkg checksums): package_name

  This error can break Dockerfile builds but is expected behavior from the kernel and is a known issue upstream (see https://github.com/docker/docker/issues/10180.)

  The workaround is to run touch /var/lib/rpm/* before installing the package. (Bug ID 21804564)

• 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

• Multi-threaded processes under ustack(), usym(), uaddr() and umod() which perform dlopen() in threads other than the first thread may not have accurate symbol resolution for symbols introduced by the dlopen(). (Bug ID 20045149)

• The lxc-net service does not always start immediately after installation on Oracle Linux 6

  The lxc-net service does not always start immediately after installation on Oracle Linux 6, even though this action is specified as part of the RPM post-installation script. This can prevent the lxcbr0 interface from coming up. If this interface is not up after installation, you can manually start it by running service lxc-net start. (Bug ID 23177405)

• LXC read-only ip_local_port_range parameter

  With lxc-1.1 or later and UEK R4, ip_local_port_range is a read-writable parameter under /proc/sys/net/ipv4 in an Oracle Linux container rather than being read-only. (Bug ID 21880467)

When booting Oracle Linux 6 on hardware with an ASPEED graphics controller, the console may appear to hang during the boot process after starting udev. However, the system does boot properly and is accessible. The workaround is to add nomodeset as a kernel boot parameter in /etc/grub.conf. (Bug ID 22389972)

You can safely ignore the following error when the Oracle-supported RDMA service starts:

Loading OpenIB kernel modules:insmod: error inserting  
'/lib/modules/3.8.13-68.3.4.el6uek.x86_64/kernel/drivers/infiniband/hw/mlx4/
mlx4_ib.ko': -1 File exists

The message indicates that the mlx4_ib module is already loaded. (Bug ID 21410136)

An Oracle Linux 6 system with the oracle-ofed-release packages installed and an iSER (iSCSI Extensions for RDMA) target configured, hangs and generates an Out-Of-Memory error when the initiator logs into the iSER target disk. The login fails and the target system hangs. The following error is displayed on the remote console:

Out of memory: Kill process ...

The cause is under investigation and there is no known workaround at this time. (Bug ID 22230403)

Quotas are disabled on XFS if the file system is remounted with read-only permissions on Oracle Linux 6. (Bug ID 22908906)

NFS is not designed to handle OFD locking. (Bug ID 22948696).

The SRQ function that optimizes resource usage within the rds_rdma module is experimental and is disabled by default. A warning message is displayed when you enable this feature by setting the rds_ib_srq_enabled flag. (Bug ID 23523586).

Once the rds_rdma module has been loaded, you cannot remove the module using either rmmod or modprobe -r. Unloading of the rds_rdma module is unsupported and can trigger a kernel panic. Do not set the module_unload_allowed flag for this module. (Bug ID 23580850).

Oracle Infiniband HCAs that require the sif (Scalable Interface) driver to be loaded must have sufficient memory available to support each interface. The sif driver requires at least 30 MB of memory for the driver itself and then 50 MB of memory per interface in SR-IOV PF and VF conditions. This is particularly important when loading this driver on Oracle VM Server 3.4.1 and above, since the default memory allocation for dom0 may not be sufficient to support multiple psif instances and could result in "Out of memory" errors. To resolve this issue, increase the memory allocated to dom0 on Oracle VM Server. (Bug ID 23523713)

Oracle VM Servers running UEKR4u2 and upward in dom0 require at least 400MB more memory to use the Mellanox drivers. This is because the default size of the SRQ count was increased from 64K to 256K in later versions of the kernel and the scale_profile option is now enabled by default in the mlx_core module.

In the case where "Out of memory" errors are observed in dom0, the maximum dom0 memory size should be increased. Alternative workarounds may involve manually setting the module parameters for the mlx4_core driver. To do this, edit /etc/modprobe.d/mlx4_core.conf and set scale_profile to 0. Alternately, set log_num_srq to 16. The preferred resolution to this issue is to increase the memory allocated to dom0 on Oracle VM Server. (Bug ID 23581534)

The Sockets Direct Protocol (SDP), which was designed to provide an RDMA alternative to TCP over Infiniband networks, is known to suffer from performance degradation on more recent kernels such as UEK R4 U2. There is no active development on this protocol.

Although the library for this protocol is still available for this kernel, support is limited. You should consider using TCP on top of IP over Infiniband as a more stable alternative. (Bug ID 22354885)