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Session ID: O24. Enterprise Volume Management System for Linux. Steve Dobbelstein. Lake Buena Vista, FL September 8-12, 2003. © IBM Corporation 2003. Trademark Notes.

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Session ID: O24

Enterprise Volume Management System for Linux

Steve Dobbelstein

Lake Buena Vista, FL September 8-12, 2003

© IBM Corporation 2003


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Trademark Notes

  • The following terms are trademarks of International Business Machines Corporation in the United States and/or other countries:

    • IBM

    • AIX

    • OS/2

    • System/390

  • Linux is a trademark of Linus Torvalds

  • Other company, product, and service names may be trademarks or service marks of others.


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Agenda

  • Volume management basics

    • Overview of volume management schemes

  • Enterprise Volume Management System (EVMS)

    • Overview

    • Demonstration


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What is Volume Management?

  • Provide a logical abstraction of the physical storage devices

  • File systems and applications do not need to know about the organization of the physical devices


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Where To Use Volume Management

  • Systems with lots of physical storage

    • Lots of disks (tens, hundreds, thousands)

    • Combine many disks into a single pool of storage

      • Increased total storage space

      • Redundancy to protect against hardware failures

  • Systems with little physical storage

    • Single disk (most PCs, laptops)

    • Divide up disk to provide logically separate storage for different uses


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Disk Partitioning

  • Divide a disk into one or more logical sections

  • Simple, widely used

  • Fixed sizes, difficult to resize

  • No redundancy


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RAID

  • Redundant Array of Inexpensive Disks

  • Combine several disks

    • Increase total storage space

    • Provide redundancy

    • Improve performance

  • Can be done in hardware or software


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RAID Linear

  • Linear concatenation of several disks

  • Increased total storage space

  • No redundancy or performance improvement


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RAID 0

  • Striping

    • Data are interleaved across all disks

  • Increased total storage space

  • Improved performance with parallel I/O

  • No redundancy


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RAID 1

  • Mirroring

  • Redundancy

    • Multiple copies of all data

  • No extra storage space

    • Device size is equal to a single disk

  • Improved read performance

  • Reduced write performance


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RAID 4

  • Striping with parity

  • Redundancy, but less than with mirroring

    • One "chunk" of parity bits per stripe

  • Increased storage space (minus size of one disk)

  • Improved performance, but at cost of CPU overhead


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RAID 5

  • RAID 4 creates a bottleneck on the parity disk

  • Spread parity among all disks for better performance

  • Same total size as RAID 4


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Volume Groups

  • A collection of devices (disks, partitions, RAID)

  • The space of all devices is combined in the group, but not directly available as a device.


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Volume Groups

  • Combined space is divided into fixed-sized chunks

    • Physical Extents (PEs)

    • Similar to memory page frames


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Volume Groups

  • Create volumes from free-space in the group

  • Volumes consist of Logical Extents (LEs)

    • Each LE maps to a PE


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Volume Groups

  • Simple resizing of groups

    • Add new devices to the group to expand total available free-space

    • Remove devices that aren't used by any volumes


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Volume Groups

  • Simple resizing of volumes

    • Add or remove extents at the end of the volume


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Snapshots

  • Frozen image of a live volume

    • Useful for performing consistent backups without needing to take file system off-line

  • Copy-On-Write to save old data

  • "Origin" volume is always up-to-date

  • Snapshot capacity can be smaller than origin

  • Multiple simultaneous snapshots of same origin


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Snapshots

  • Origin volume and snapshot storage are divided into equal sized “chunks”


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Snapshots

  • Write to the origin volume


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Snapshots

  • Write to the origin volume

    • Write request is queued to be finished later

    • Chunk is read from the origin


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Snapshots

  • Write to the origin volume

    • Write chunk to snapshot storage


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Snapshots

  • Write to the origin volume

    • New COW table entry: Map chunk 4 to chunk 1


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Snapshots

  • Write to the origin volume

    • Release all I/Os waiting on this copy


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Snapshots

  • Read from the snapshot volume

    • Unmapped chunk: get data from origin volume


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Snapshots

  • Read from the snapshot volume

    • Re-mapped chunk: get data from snapshot


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Bad Block Relocation

  • Detect I/O errors

  • Remap bad blocks to a reserved area of the device


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Enterprise Volume Management System

  • Modular, extensible system for managing storage on Linux

  • Integrates all aspects of volume management into a single package

    • Disk Partitioning (fdisk, Disk Druid)

    • Volume Groups (LVM)

    • Software RAID (MD)

    • File Systems (mkfs, fsck, resizefs)

    • More



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EVMS Architecture

  • Engine

    • Core library

      • Provides API for user interfaces

    • Coordinates all activities with the plug-ins

    • Defines common set of possible tasks

      • Creation

      • Deletion

      • Resize

      • Configuration changes



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EVMS Engine Architecture

  • Volume discovery bubbles up through the layers

    • Local Disk Manager plug-in discovers all disk devices

    • Each plug-in examines current list of devices

      • Claims a device by removing from the list

      • Creates new devices and adds to the list


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EVMS Engine Architecture

  • Plug-ins

    • Each plug-in recognizes a specific volume format

      • Partitions

      • Volume Groups

      • Software RAID

      • EVMS Features

      • File Systems



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EVMS User Interfaces

  • Communicate with Engine through well-defined API

  • Graphical User Interface (evmsgui)

    • Point-and-click

    • Intuitive displays

  • Text-Mode (evmsn)

    • Graphical-like for terminal windows

    • Same look and feel of the GUI

  • Command-Line (evms)

    • Create scripts for common tasks


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Clustering Support in EVMS

  • EVMS can operate in a cluster of machines

    • Assign ownership to a group of disks

      • Private to one cluster node

      • Shared by all cluster nodes

      • Reassign ownership during fail-over

    • Remote Administration

      • Ability to administer other nodes in the cluster from a single machine


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Clustering Support in EVMS

  • Cluster Managers

    • Provide membership and communication services

    • Used to specify fail-over policies

    • Linux-HA

      • Open-source, High-Availability cluster manager

    • RSCT

      • Reliable Scalable Cluster Technology

  • OpenGFS (in development)

    • Open-source cluster file system

    • Mount a file system on all cluster nodes simultaneously


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EVMS Platform Support

  • EVMS has been tested on Linux running on:

    • xSeries

      • x86

      • IA64

    • pSeries

      • PPC

      • PPC64

    • zSeries

      • s390

      • s390x


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Summary of EVMS Capabilities

  • EVMS integrates all aspects of disk, partition, and volume management into a single, easy-to-use system.

  • EVMS has no design limits on the number of disks, partitions, or volumes that it can handle.

  • EVMS minimizes down time due to configuration changes.

  • EVMS is very extensible, due to its modular design and support of plug-in modules.

  • (continued)


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Summary of EVMS Capabilities

  • EVMS is designed to be scalable, including use in clustering environments.

  • EVMS can read, write, and manipulate volumes created by other volume managers (given the proper plug-ins).

  • EVMS can reduce the costs associated with migrating data to Linux.


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EVMS Project Information

  • Hosted on SourceForge

    • http://evms.sf.net

    • Live CVS tree

    • Mailing lists

      • [email protected]

      • [email protected]

    • Installation instructions

    • Documentation

      • http://evms.sf.net/docs/EVMS-xSeries-2003.ppt

  • IRC: irc.freenode.net, #evms



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