Chapter 1. Overview of EVMS

The Enterprise Volume Management System (EVMS) 2.5.5 management tool for Linux is an extensible storage management tool that integrates all aspects of volume management, such as disk partitioning, the Logical Volume Manager (LVM), the Multiple-Disk (MD) manager for software RAIDs, the Device Mapper (DM) for multipath I/O configuration, and file system operations.

1.1. Benefits of EVMS

EVMS provides the following benefits:

  • An open source volume manager

  • A plug-in framework for flexible extensibility and customization

  • Plug-ins to extend functionality for new or evolving storage managers

  • Support for foreign partition formats

  • Cluster-aware

1.2. Plug-In Layers

EVMS abstracts the storage objects in functional layers to make storage management more user-friendly. The following table describes the current EVMS plug-in layers for managing storage devices and file systems:

Table 1.1. EVMS Plug-In Layers

Storage Managers

Description

Plug-Ins

Device

Manages the physical and logical devices

Device Mapper (DM)

Segment

Manages the partitioning of physical and logical devices into smaller segments of free space.

Segment managers can be stacked. For example, a cluster segment can contain other storage objects or volumes.

Uses Device Mapper (DM)

Segment managers include DOS, GPT, System/390 (S/390), Cluster, BSD, Mac, and BBR

For more information, see Section 4.1, “Understanding Disk Segmentation”.

Regions

Manages the combination of multiple storage objects

LVM/LVM2 for containers and region, MD for RAIDs, and DM for multipath I/O

EVMS Features

Manages EVMS features

Drive linking (linear concatenation), Bad Block Relocation (BBR), and Snapshot

File System Interface Modules (FSIM)

Manages the interface between the file system managers and the segment managers

For information, see Section 1.3, “Supported File Systems”.

Cluster Manager Interface Modules

Manages the interface between the cluster manager and the file systems and devices

HeartBeat 2


1.3. Supported File Systems

EVMS supports the following Linux file systems:

  • EXT3

  • ReiserFS

  • XFS

  • OCFS2

  • JFS

  • EXT2

  • Swap

  • NTFS (read only)

  • FAT (read only)

For more information about file systems supported in SUSE Linux Enterprise Server 10, see the SUSE Linux Enterprise Server 10 Installation and Administration Guide..

The Novell Storage Services (NSS) file system is also supported when used with the Novell Open Enterprise Server 2 for SUSE Linux Enterprise Server 10 SP1 (or later versions of OES 2 and SLES 10).

The File System Primer describes the variety of file systems available on Linux and which ones are the best to use for which workloads and data.

1.4. Terminology

EVMS uses the following terminology in the EVMS user interface:

Table 1.2. EVMS Terms

Term

Description

Sector

The lowest level that can be addressed on a block device.

Disk

A physical disk or a logical device.

Segment

An ordered set of physically contiguous sectors on a single device. It is similar to traditional disk partitions.

Region

An ordered set of logically contiguous sectors that might or might not be physically contiguous. The underlying mapping can be to logical disks, disk segments, or other storage regions.

Feature

(Feature Object, EVMS Feature, EVMS Object)

A logically contiguous address space created from one or more disks, segments, regions, or other feature objects through the use of an EVMS feature.

Storage Object

Any storage structure in EVMS that is capable of being a block device. Disks, segments, regions, and feature objects are all storage objects.

Container

(Storage Container)

A collection of devices that is managed as a single pool of storage.

Private Storage Container: A storage container that is exclusively owned and accessed by only one server.

Cluster Storage Container: A storage container managed by the Cluster Resource Manager. It is accessible to all nodes of a cluster. An administrator can configure the storage objects in the cluster container from any node in the cluster. Cluster containers can be private, shared, or deported.

  • Private: The cluster container is exclusively owned and accessed by only one particular node of a cluster at any given time. The ownership can be reassigned by failover policies or the administrator.

  • Shared: The cluster container is concurrently owned and accessed by all nodes of a cluster. Shared containers are preferred for distributed databases, clustered file systems, and cluster-aware applications that can coordinate safe access to shared volumes.

  • Deported: The cluster container is not owned or accessed by any node of the cluster.

Volume

(Logical Volume)

A mountable storage object. Logical volumes can be EVMS volumes or compatibility volumes.

  • EVMS Volume: Volumes that contain EVMS metadata and support all EVMS features. Device nodes for EVMS volumes are stored in the /dev/evms directory. For example: /dev/evms/my_volume

  • Compatibility Volume: Volumes that are backward-compatible to other volume managers. They do not contain EVMS metadata and cannot support EVMS features.


1.5. Location of Device Nodes for EVMS Storage Objects

EVMS creates a unified namespace for the logical volumes on your system in the /dev/evms directory. It detects the storage objects actually present on a system, and creates an appropriate device node for each one, such as those shown in the following table.

Table 1.3. Device Node Location

Storage Object

Standard Location the Device Node

EVMS Location of the Device Node

A disk segment of disk

/dev/sda5

/dev/evms/sda5

A software RAID device

/dev/md1

/dev/evms/md/md1

An LVM volume

/dev/lvm_group/lvm_volume

/dev/evms/lvm/lvm_group/lvm_volume


SUSE® Linux Enterprise Server Storage Administration Guide 10 SP3/SP4