Chapter 9. Storage
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 …).
-s/--snapshot option in the lvcreate man page.
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 LV. 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 man page.
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.
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.
use_lvmetad parameter in the /etc/lvm/lvm.conf file, and enable the lvmetad daemon by configuring the lvm2-lvmetad init script.
Fiber Channel over Ethernet (FCoE) target mode is fully supported in Red Hat Enterprise Linux 6.3. This kernel feature is configurable via the targetcli utility, supplied by the fcoe-target-utils package. FCoE is designed to be used on a network supporting Data Center Bridging (DCB). Further details are available in the dcbtool(8) and targetcli(8) man pages (provided by the lldpad and fcoe-target-utils packages, respectively).
The expanded RAID support in LVM is now fully supported in Red Hat Enterprise Linux 6.3. LVM is now capable of creating RAID 4/5/6 logical volumes and supports mirroring of these logical volumes. The MD (software RAID) modules provide the backend support for these new features.
A new LVM configuration file parameter, activation/read_only_volume_list, makes it possible to always activate particular volumes in read-only mode, regardless of the actual permissions on the volumes concerned. This parameter overrides the --permission rw option stored in the metadata.
