Chapter 2. Technology Previews

A new implementation of LVM copy-on-write (cow) snapshots is available in Red Hat Enterprise Linux 6.3 as a Technology Preview. The main advantage of this implementation, compared to the previous implementation of snapshots, is that it allows many virtual devices to be stored on the same data volume. This implementation also provides support for arbitrary depth of recursive snapshots (snapshots of snapshots of snapshots …).

This feature is for use on a single system. It is not available for multi-system access in cluster environments.

For more information, refer to the documentation of the -s/--snapshot option in the lvcreate man page.

Package: lvm2-2.02.95-10

Logical Volumes (LVs) can now be thinly provisioned to manage a storage pool of free space to be allocated to an arbitrary number of devices when needed by applications. This allows creation of devices that can be bound to a thinly provisioned pool for late allocation when an application actually writes to the pool. The thinly-provisioned pool can be expanded dynamically if and when needed for cost-effective allocation of storage space. In Red Hat Enterprise Linux 6.3, this feature is introduced as a Technology Preview. You must have the device-mapper-persistent-data package installed to try out this feature. For more information, refer to the lvcreate(8) man page.

Package: lvm2-2.02.95-10

Most LVM commands require an accurate view of the LVM metadata stored on the disk devices on the system. With the current LVM design, if this information is not available, LVM must scan all the physical disk devices in the system. This requires a significant amount of I/O operations in systems that have a large number of disks.

The purpose of the lvmetad daemon is to eliminate the need for this scanning by dynamically aggregating metadata information each time the status of a device changes. These events are signaled to lvmetad by udev rules. If lvmetad is not running, LVM performs a scan as it normally would.

This feature is provided as a Technology Preview and is disabled by default in Red Hat Enterprise Linux 6.3. To enable it, refer to the use_lvmetad parameter in the /etc/lvm/lvm.conf file, and enable the lvmetad daemon by configuring the lvm2-lvmetad init script.

Package: lvm2-2.02.95-10

Parallel NFS (pNFS) is a part of the NFS v4.1 standard that allows clients to access storage devices directly and in parallel. The pNFS architecture eliminates the scalability and performance issues associated with NFS servers in deployment today.

pNFS supports 3 different storage protocols or layouts: files, objects and blocks. The Red Hat Enterprise Linux 6.3 NFS client supports the files layout protocol.

To automatically enable the pNFS functionality, create the /etc/modprobe.d/dist-nfsv41.conf file with the following line and reboot the system:

alias nfs-layouttype4-1 nfs_layout_nfsv41_files

Now when the -o minorversion=1 mount option is specified, and the server is pNFS-enabled, the pNFS client code is automatically enabled.

For more information on pNFS, refer to http://www.pnfs.com/.

Package: kernel-2.6.32-279

Open Multicast Ping (Omping) is a tool to test the IP multicast functionality, primarily in the local network. This utility allows users to test IP multicast functionality and assists in the diagnosing if an issues is in the network configuration or elsewhere (that is, a bug). In Red Hat Enterprise Linux 6 Omping is provided as a Technology Preview.

Package: omping-0.0.4-1

The System Information Gatherer and Reporter (SIGAR) is a library and command-line tool for accessing operating system and hardware level information across multiple platforms and programming languages. In Red Hat Enterprise Linux 6.3, SIGAR is considered a Technology Preview package.

Package: sigar-1.6.5-0.4.git58097d9

Red Hat Enterprise Linux 6 includes fsfreeze as a Technology Preview. fsfreeze is a new command that halts access to a file system on a disk. fsfreeze is designed to be used with hardware RAID devices, assisting in the creation of volume snapshots. For more details on the fsfreeze utility, refer to the fsfreeze(8) man page.

Package: util-linux-ng-2.17.2-12.7

DIF/DIX, is a new addition to the SCSI Standard and a Technology Preview in Red Hat Enterprise Linux 6. 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 receive, and stores both the data and the checksum. Conversely, when a read occurs, the checksum can be checked by the storage device, and by the receiving HBA.

The DIF/DIX hardware checksum feature must only be used with applications that exclusively issue O_DIRECT I/O. These applications may use the raw block device, or the XFS file system in O_DIRECT mode. (XFS is the only file system that does not fall back to buffered I/O when doing certain allocation operations.) Only applications designed for use with O_DIRECT I/O and DIF/DIX hardware should enable this feature.

For more information, refer to section Block Devices with DIF/DIX Enabled in the Storage Administration Guide.

Package: kernel-2.6.32-279

Filesystem in Userspace (FUSE) allows for custom file systems to be developed and run in user space.

Package: fuse-2.8.3-4

Btrfs is under development as a file system capable of addressing and managing more files, larger files, and larger volumes than the ext2, ext3, and ext4 file systems. Btrfs is designed to make the file system tolerant of errors, and to facilitate the detection and repair of errors when they occur. It uses checksums to ensure the validity of data and metadata, and maintains snapshots of the file system that can be used for backup or repair. The Btrfs Technology Preview is only available on AMD64 and Intel 64 architectures.

Package: btrfs-progs-0.19-12

Red Hat Enterprise Linux 6 features the new LVM application programming interface (API) as a Technology Preview. This API is used to query and control certain aspects of LVM.

Package: lvm2-2.02.95-4

FS-Cache in Red Hat Enterprise Linux 6 enables networked file systems (for example, NFS) to have a persistent cache of data on the client machine.

Package: cachefilesd-0.10.2-1

eCryptfs is a stacked, cryptographic file system. It is transparent to the underlying file system and provides per-file granularity. eCryptfs is provided as a Technology Preview in Red Hat Enterprise Linux 6.

Package: ecryptfs-utils-82-6