Storage Systems: Storage Systems: Advanced TopicsAdvanced Topics

Learning Objectives:• To understand limitations of “one file system

per partition” model• To understand Logical Volume Management –

its motivations and its facilities• To understand how Storage Area Networks

extend these features to multiple systems• To relate LVM and SAN to a most modern file

system implementation

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Storage VirtualizationStorage Virtualization

File System Code– assumes 1 file system– to 1 disk drive (partition)

Stripe/Mirror/RAID changes this

Storage Virtualization: break filesystem/drive relationship

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OSOS

Device DriversDevice Drivers

File SystemFile System

Logical Volume Logical Volume ManagementManagement

• Virtual mapping between file system code and physical device

• Analogous (but not identical!) to virtual memory addressing

• “Volume Group” of all drives in a pool• Storage space in “Volume Group” divided

into “Physical Extents” – usually all same size

• “Logical Volume” is set of “Physical Extents”

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Logical Volume Logical Volume ManagementManagement

• Mirror/Stripe/RAID provided within LVM layer

• Resize filesystem

• “Snapshot” a live filesystem

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OSOS

Device DriversDevice Drivers

File SystemFile System

LVM layerLVM layer

Volume Group

e.g. Linux Servere.g. Linux Server

• / - mostly read – want fast seeks

• swap – read/write – want high bandwidth

• /opt – infrequent access

• /var – huge, infrequent access

• Mirror /

• Stripe swap

• spare space to /opt and /var

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LVM Example:LVM Example:

• Now we can share resources more flexibly and more efficiently – but only on one server

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Storage Area Storage Area NetworkingNetworking

• Implement LVM features in separate storage controller

• Connect multiple servers to storage controller• via SCSI, or FibreChannel, or Infiniband, or

…(n.b. SAN over Ethernet is conventionally called Networked Attached Storage (NAS)

• Now can share disk resources across multiple servers

• Rapid migration of disk images

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Storage Area Network Storage Area Network ControllerController

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8 “Blade Servers”

SA

N

Con

trol

ler

SA

N

Con

trol

ler

SAN Key FeaturesSAN Key Features

• Functionality– Key element of “system virtualization”– Migrating virtual machines– “De-duping” – share common subsets of

file systems (think Virtual Machine images!)

• Management:– Manage storage separately from server

physical resources– Maximize flexibility of storage provisioning

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ZFS – Volume Aware ZFS – Volume Aware File SystemFile System

Marketing claims:

• Lost a file?

• Run out of space?

• Difficult disk upgrade?

• Want to grow/shrink?

• Data Corruption?

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Pools of storage

ZFS techniquesZFS techniques

• Lost a file?– Copy-on-write – simple rollback/recovery

• Run out of space/Difficult disk upgrade?– Add new storage to live systems– Self-checking, self-healing

• Want to grow/shrink?

• Data Corruption?– end-to-end sumchecking

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ZFS ImplementationZFS Implementation

• ZFS Combines File Service and Logical Volume Management

• Is this a good idea?

Discuss

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