Design of a Cluster Logical Volume Manager

Design of a Cluster Logical Volume Manager

Abstract:

Logical Volume Managers provide a higher level view of disk storage on a computer system than the traditional view of disks and partitions. However the functionality of the existing logical volume managers is restricted to a single machine and they cannot be easily incorporated in a cluster environment. This is because logical volume managers today do not support distributed updates and locking on metadata. I propose a design of a Cluster Logical Volume Manager which incorporates a distributed locking mechanism on metadata to enforce a single node exclusive access to cluster metadata. The design can be incorporated in practically all the logical volume managers available today. As a case study, I have proposed a design for the Cluster Logical Volume Manager, which enhances the Linux Logical Volume Manager to function in a cluster. The design incorporates a cluster lock manager in the architecture, which ensures that the metadata operations are handled very carefully ensuring stability of the cluster data.

What is a Logical Volume Manager?

In an open systems environment, logical volume manager (LVM) virtualizes storage by consolidating physical storage into logical volumes, which are available to applications or file systems. LVMs are available on most Unix platforms (including Linux) and on Windows 2000. By assembling virtual storage volumes out of numerous physical devices, you can create storage configurations tuned for specific applications, without the limitations of specific hardware devices. Instead, you can make use of the available storage, without locking into proprietary storage solutions. Logical volume managers improve application availability by building redundancy into the logical volume itself. The possibilities go beyond simple mirroring and RAID. For example, the failure of a device in a redundant storage configuration can degrade performance and expose the data to risk from another failure. The logical volume manager can maintain a pool of spare disks that can be automatically swapped in (hot relocation) when a device fails in a logical volume. It can even move data back automatically when the failed device is replaced or repaired. Unlike a physical device, a logical volume has a nearly limitless capacity: Administrators can add storage as needed without interrupting access to the data. When used with a database's auto-extend capabilities or a file system's automatic extension, a logical volume manager can significantly ease the problem of provisioning storage for growing applications.
LVM supports enterprise level volume management of disk and disk subsystems by grouping arbitrary disks into volume groups. The total capacity of volume groups can be allocated to logical volumes, which are accessed as regular block devices. Further, LVM provides logical separation of storage, the ability to move data from one physical device to another while on-line, and dynamic block device resizing. LVM also enables system administrators to upgrade systems, remove failing disks, reorganize workloads, and adapt to changing system needs, through a minimum amount of time and effort. LVM is a major building block for the Linux OS because it allows Linux to be used in an enterprise server environment. In addition to addressing the needs of the enterprise computing sector, LVM provides ease-of-use for desktop users as well, by simplifying on-disk management of Linux file systems and volumes.


for more info visit.
http://www.enjineer.com