4. Filesystems and Storage updates

In the 5.4 update, several significant additions have been made to file systems support. Base Red Hat Enterprise Linux now includes the Filesystem in Userspace (FUSE) kernel modules and user space utilities, allowing users to install and run their own FUSE file systems on an unmodified Red Hat Enterprise Linux kernel (BZ#457975). Support for the XFS file system has also been added to the kernel for future product enablement (BZ#470845). The FIEMAP input/output control (ioctl) interface has been implemented, allowing the physical layout of files to be mapped efficiently. The FIEMAP ioctl can be used by applications to check for fragmentation of a specific file or to create an optimized copy of a sparsely allocated file (BZ#296951).

Additionally, the Common Internet File System (CIFS) has been updated in the kernel (BZ#465143). The ext4 file system (included in Red Hat Enterprise Linux as a Technology Preview) has also been updated (BZ#485315).

In Red Hat Enterprise Linux 5.4, the use of the Global File System 2 (GFS2) as a single server file system (i.e. not in a clustered environment) is deprecated. Users of GFS2 that do not need high availability clustering are encouraged to look at migrating to other file systems like the ext3 or xfs offerings. The xfs file system is specifically targeted at very large file systems (16 TB and above). Existing users will continue to be supported.

The required semantics indicate that a process which completes a stat, write, stat, should see a different mtime (time of last modification) on the file in the results from the second stat call compared to the mtime in the results from the first stat call. File times in NFS are maintained strictly by the server, so the file mtime will not be updated until the data has been transmitted to the server via the WRITE NFS protocol operation. Simply copying data into the pagecache is not sufficient to cause the mtime to be updated. This is one place where NFS differs from local file systems. Therefore, an NFS filesystem which is under a heavy write workload may result in stat calls having a high latency.(BZ#469848)

The ext4 filesystem Technology Preview has been refreshed with updated userspace tools. Ext4 is an incremental improvement on the ext3 file system developed by Red Hat and the Linux community.

With this update, the dmraid logwatch-based email reporting feature has been moved from the dmraid-events package into the new dmraid-events-logwatch package. Consequently, systems that use this dmraid feature will need to complete the following manual procedure: (BZ#512833)

samba3x and ctdb are provided as a Technology Preview on the x86_64 platform. Samba3x package provides Samba 3.3 and ctdb provide a clustered TDB backend. Running samba3x and ctdb on a set of cluster nodes with GFS file system will allow the export of a clustered CIFS filesystem.