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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

trademark notes
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.
  • Volume management basics
    • Overview of volume management schemes
  • Enterprise Volume Management System (EVMS)
    • Overview
    • Demonstration
what is volume management
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
where to use volume management
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
disk partitioning
Disk Partitioning
  • Divide a disk into one or more logical sections
  • Simple, widely used
  • Fixed sizes, difficult to resize
  • No redundancy
  • Redundant Array of Inexpensive Disks
  • Combine several disks
    • Increase total storage space
    • Provide redundancy
    • Improve performance
  • Can be done in hardware or software
raid linear
RAID Linear
  • Linear concatenation of several disks
  • Increased total storage space
  • No redundancy or performance improvement
raid 0
  • Striping
    • Data are interleaved across all disks
  • Increased total storage space
  • Improved performance with parallel I/O
  • No redundancy
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
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
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
volume groups
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.
volume groups14
Volume Groups
  • Combined space is divided into fixed-sized chunks
    • Physical Extents (PEs)
    • Similar to memory page frames
volume groups15
Volume Groups
  • Create volumes from free-space in the group
  • Volumes consist of Logical Extents (LEs)
    • Each LE maps to a PE
volume groups16
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
volume groups17
Volume Groups
  • Simple resizing of volumes
    • Add or remove extents at the end of the volume
  • 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
  • Origin volume and snapshot storage are divided into equal sized “chunks”
  • Write to the origin volume
  • Write to the origin volume
    • Write request is queued to be finished later
    • Chunk is read from the origin
  • Write to the origin volume
    • Write chunk to snapshot storage
  • Write to the origin volume
    • New COW table entry: Map chunk 4 to chunk 1
  • Write to the origin volume
    • Release all I/Os waiting on this copy
  • Read from the snapshot volume
    • Unmapped chunk: get data from origin volume
  • Read from the snapshot volume
    • Re-mapped chunk: get data from snapshot
bad block relocation
Bad Block Relocation
  • Detect I/O errors
  • Remap bad blocks to a reserved area of the device
enterprise volume management system
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
evms architecture30
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
evms engine architecture32
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
evms engine architecture33
EVMS Engine Architecture
  • Plug-ins
    • Each plug-in recognizes a specific volume format
      • Partitions
      • Volume Groups
      • Software RAID
      • EVMS Features
      • File Systems
evms user interfaces
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
clustering support in evms
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
clustering support in evms37
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
evms platform support
EVMS Platform Support
  • EVMS has been tested on Linux running on:
    • xSeries
      • x86
      • IA64
    • pSeries
      • PPC
      • PPC64
    • zSeries
      • s390
      • s390x
summary of evms capabilities
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)
summary of evms capabilities40
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.
evms project information
EVMS Project Information
  • Hosted on SourceForge
    • Live CVS tree
    • Mailing lists
    • Installation instructions
    • Documentation
  • IRC:, #evms